U.S. patent application number 10/915011 was filed with the patent office on 2005-01-13 for thermoplastic elastomer compositions rheology-modified using peroxides and free radical coagents.
Invention is credited to Walton, Kim Louis.
Application Number | 20050009942 10/915011 |
Document ID | / |
Family ID | 26928108 |
Filed Date | 2005-01-13 |
United States Patent
Application |
20050009942 |
Kind Code |
A1 |
Walton, Kim Louis |
January 13, 2005 |
Thermoplastic elastomer compositions rheology-modified using
peroxides and free radical coagents
Abstract
Rheology-modified thermoplastic elastomer compositions
comprising a melt blend of an ethylene/a-olefin polymer and a high
melting polymer such as polypropylene or a propylene/a-olefin
copolymer wherein the rheology modification is induced by a
combination of a peroxide and a free radical coagent. The resulting
compositions have an elastomeric phase, a non-elastomeric phase and
certain physical properties that exceed those of a like composition
that is rheology-modified by peroxide alone. The compositions can
be used to make a variety of articles of manufacture, such as
automotive instrument panel skins, via calendaring and
thermoforming procedures.
Inventors: |
Walton, Kim Louis; (Lake
Jackson, TX) |
Correspondence
Address: |
DUPONT DOW ELASTOMERS, LLC
PATENT RECORDS CENTER
4417 LANCASTER PIKE
BARLEY MILL PLAZA 25
WILMINGTON
DE
19805
US
|
Family ID: |
26928108 |
Appl. No.: |
10/915011 |
Filed: |
August 9, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10915011 |
Aug 9, 2004 |
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10361296 |
Feb 10, 2003 |
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6774186 |
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10361296 |
Feb 10, 2003 |
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09951056 |
Sep 13, 2001 |
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6548600 |
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60234599 |
Sep 22, 2000 |
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Current U.S.
Class: |
521/134 ;
525/192; 525/240 |
Current CPC
Class: |
C08L 2205/02 20130101;
C08L 23/10 20130101; C08L 23/0815 20130101; C08K 5/0025 20130101;
C08K 5/14 20130101; C08K 5/0025 20130101; C08L 23/16 20130101; C08K
5/14 20130101; C08L 23/16 20130101; C08L 23/0815 20130101; C08L
2666/04 20130101; C08L 23/10 20130101; C08L 2666/04 20130101 |
Class at
Publication: |
521/134 ;
525/192; 525/240 |
International
Class: |
C08L 023/00; C08L
023/04 |
Claims
What is claimed is:
1. A rheology-modified, substantially gel-free thermoplastic
elastomer composition comprising at least one elastomeric
ethylene/alpha-olefin polymer or ethylene/alpha-olefin polymer
blend and at least one high melting polymer selected from the group
consisting of polypropylene homopolymers and propylene/ethylene
copolymers, wherein the rheology modification is induced by a
combination comprising a peroxide and a free radical coagent and
the composition has a melt toughness of at least about 600 cNmm/s,
a true ultimate tensile strength at 140.degree. C. of at least
about 3 MPa and an elongation to break at 140.degree. C. of least
about 400%.
2. The composition of claim 1 wherein the peroxide is an organic
peroxide.
3. The composition of claim 2 wherein the organic peroxide is
selected from the group consisting of
.alpha.,.alpha.'-bis(t-butylperoxy)-diisopro- pylbenzene, dicumyl
peroxide, di-(t-amyl)peroxide, 2,5-dimethyl-2,5-di(t-b-
utylperoxy)hexyne-3,2,5-dimethyl-2,5-di(t-butylperoxy)hexane,
2,5(t-amyl peroxy-2-ethylhexonate), 2,5-dimethyl-2,5-di-(t-butyl
peroxy)hexane, di-t-butylperoxide, 2,5-di(t-amyl
peroxy)-2,5-dimethylhexane,
2,5-di-(t-butylperoxy)-2,5-diphenylhexane,
bis(alpha-methylbenzyl)peroxid- e, t-butyl perbenzoate, benzoyl
peroxide, 3,6,9-triethyl-3,6,9-trimethyl-1- ,4,7-triperoxonane and
bis(t-butylperoxy)-diisopropylbenzene.
4. The composition of claim 1 wherein the free radical coagent is
selected from the group consisting of diallyl terephthalate,
triallylcyanurate, triallylisocyanurate, 1,2-polybutadiene, divinyl
benzene, trimethylolpropane trimethacrylate, polyethylene glycol
dimethacrylate, ethylene glycol dimethacrylate, pentaerythritol
triacrylate, allyl methacrylate, N,N'-m-phenylene bismaleimide,
toluene bismaleimide-p-quinone dioxime, nitrobenzene, and
diphenylguanidine.
5. The composition of claim 4 wherein the free radical coagent is
selected from the group consisting of triallylcyanurate,
1,2-polybutadiene, divinyl benzene, and trimethylolpropane
trimethacrylate.
6. The composition of claim 1, wherein the ethylene/.alpha.-olefin
polymer has polymerized therein at least one .alpha.-olefin
comonomer, the .alpha.-olefin containing from 3 to 20 carbon
atoms.
7. The composition of claim 6, wherein the .alpha.-olefin contains
from 3 to 10 carbon atoms.
8. The composition of claim 1, wherein the ethylene/.alpha.-olefin
polymer is a diene-modified polymer, the diene being selected from
the group consisting of norbornadiene, dicyclopentadiene,
1,4-hexadiene, piperylene or 5-ethylidene-2-norbornene and mixtures
thereof.
9. The composition of claim 1, wherein the high melting polymer is
a nucleated polymer.
10. The composition of claim 1, further comprising a process oil in
an amount within a range of from greater than 0 to about 50 weight
percent, based on total composition weight.
11. The composition of claim 1 or claim 10, further comprising a
filler in an amount within a range of from about 0 to about 70
weight percent, based on total composition weight.
12. The composition of claim 1 or claim 10, further comprising a
blowing agent in an amount within a range of from greater than 0 to
about 10 weight percent, based on total composition weight.
13. The composition of claim 11, further comprising a blowing agent
in an amount within a range of from greater than 0 to about 10
weight percent, based on total composition weight.
14. A process for preparing a rheology-modified, substantially
gel-free TPE composition, the process comprising: a) adding at
least one peroxide and at least one free radical coagent to a
molten polymer blend that comprises an elastomeric
ethylene/alpha-olefin polymer and a high melting polymer selected
from the group consisting of polypropylene homopolymers and
propylene/ethylene copolymers; and b) maintaining the polymer blend
in a molten state while subjecting it to conditions of shear
sufficient to disperse the peroxide and coagent throughout the
molten polymer blend, effect rheology modification of the polymers
and substantially preclude formation of insoluble polymer gels,
sufficient rheology modification being measured by a melt toughness
of at least about 600 cNmm/s, a true ultimate tensile strength at
140.degree. C. of at least about 3 MPa and an elongation to break
at 140.degree. C. of least about 400%.
15. A process for preparing a rheology-modified, substantially
gel-free TPE composition, the process comprising: a) adding at
least one peroxide and at least one free radical coagent to at
least one component of a polymer blend that comprises an
elastomeric ethylene/alpha-olefin polymer and a high melting
polymer selected from the group consisting of polypropylene
homopolymers and propylene/ethylene copolymers; and b) converting
the polymer blend to a molten polymer blend while subjecting the
blend to conditions of shear sufficient to disperse the peroxide
and coagent throughout the molten polymer blend, effect rheology
modification of the polymers and substantially preclude formation
of insoluble polymer gels, sufficient rheology modification being
measured by a melt toughness of at least about 600 cNmm/s, a true
ultimate tensile strength at 140.degree. C. of at least about 3 MPa
and an elongation to break at 140.degree. C. of least about
400%.
16. A process for preparing a rheology-modified, substantially
gel-free thermoplastic elastomer article of manufacture, the
process comprising: a) adding at least one peroxide and at least
one free radical coagent to a molten elastomeric
ethylene/alpha-olefin polymer or elastomeric ethylene/alpha-olefin
polymer blend to provide a rheology-modified ethylene/alpha-olefin
polymer or ethylene/alpha-olefin polymer blend; b) adding to the
rheology-modified polymer or polymer blend a high melting polymer
selected from the group consisting of polypropylene homopolymers
and propylene/ethylene copolymers to form a composite polymer
blend; and c) converting the composite polymer blend into the
article of manufacture, the article of manufacture having a melt
toughness of at least about 600 cNmm/s, a true ultimate tensile
strength at 140.degree. C. of at least about 3 MPa and an
elongation to break at 140.degree. C. of least about 400%.
17. The process of any of claims 14-16, wherein the melt toughness
of the rheology-modified composition is at least 700 cNmm/s.
18. The process of claim 17, wherein the melt toughness of the
rheology-modified composition is at least 800 cNmm/s.
19. An article of manufacture having at least one component thereof
fabricated from the composition of claim 1.
20. The article of claim 19, wherein the composition further
comprises at least one additive selected from the group consisting
of process oils, fillers and blowing agents.
21. The article of claim 20, wherein the process oil is present in
an amount within a range of from greater than 0 to about 50 percent
by weight, based on total composition weight.
22. The article of claim 20, wherein the filler is selected from
the group consisting of glass, silica, carbon black, metal
carbonates, metal sulfates, talc, clay and graphite fibers.
23. The article of claim 20, wherein the filler is present in an
amount within a range of from greater than 0 to about 70 percent by
weight, based on total composition weight.
24. The article of claim 20, wherein the blowing agent is present
in an amount within a range of from greater than 0 to about 10
percent by weight, based on total composition weight.
25. The process of claim 14 or claim 15, wherein a sequential step
c) follows b), and step c) comprises converting the rheology
modified polymer blend into an article of manufacture.
26. The process of claim 25 further comprising sequential
intermediate steps b1) and b2) that precede step c), step b1)
comprising recovery of the rheology modified polymer blend as a
solid and step b2) comprising conversion of the solid to a melt
state sufficient for fabricating the article of manufacture.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/234,599 filed Sep. 22, 2000.
FIELD OF THE INVENTION
[0002] This invention relates generally to rheology-modified
thermoplastic elastomer (TPE) compositions that comprise an
elastomeric ethylene/alpha (.alpha.)-olefin (EAO) polymer or EAO
polymer blend and a high melting propylene polymer, wherein both
components are peroxide-modified and to the preparation of the
compositions, use of such compositions in processes such as
calendaring and thermoforming to make articles of manufacture and
the resulting articles of manufacture. This invention particularly
relates to such compositions wherein the rheology modification is
induced by a combination comprising an organic peroxide and a free
radical coagent, methods for preparing the compositions, such as by
modifying a physical blend of the components, and use of such
compositions in calendaring operations and thermoforming
applications.
BACKGROUND OF THE INVENTION
[0003] Heck et al. describe rheology modified TPE compositions in
WO 98/32795. The rheology modification can be induced by various
means including peroxides and radiation. The compositions of Heck
et al. are said to exhibit a combination of four properties: shear
thinning index (STI), melt strength (MS), solidification
temperature (ST) and upper service temperature (UST). While these
compositions are useful in applications such as automotive parts
and boot shafts, improved compositions are needed for calendaring
operations and thermoforming applications.
[0004] Compositions having a high melt toughness are desired in
calendaring operations. Melt toughness, as used herein, is the
product of the melt strength and the melt extensibility. In many
instances, the calendar rolls are fed with a composition in the
form of a molten rod. This molten composition must be able to
spread across the calendar rolls. The Heck et al. compositions only
spread partially across the calendar rolls.
[0005] Compositions having a high melt toughness also are preferred
for thermoforming applications. In addition, tensile properties of
the compositions at elevated temperatures are important for these
applications. For example, one method of manufacturing instrument
panel skin material is to either calender or extrude embossed
sheeting. The sheeting is then vacuum thermoformed to the contour
of the instrument panel. One method to determine compound
thermoformability is by evaluating its elevated stress-strain
behavior. Often, flexible polypropylene thermoplastic (TPO) sheets
are thermoformed at temperatures below the melting point of the
polypropylene phase. Although the thermoforming process is one of
biaxial extension, tensile tests at the thermoforming temperatures
can be used to compare thermoforming and grain retention behavior.
The peaks and valleys of the embossed grain are areas of greater
and lesser thickness and a look at the grain shows that the valleys
are narrower and less glossy than the peak areas. When a skin is
thermoformed, the thinner areas will be subject to greater stress
and the greater applied stress in these areas concentrates the
elongation in the thinner valley areas. These areas elongate
preferentially and the attractive "narrow valley, broad peak"
appearance is lost, called "grain washout"--unless the material can
be designed to elongate more evenly. Strain hardening is the
property by which areas of material which have already been
strained become stiffer, transferring subsequent elongation into
areas which are as yet unstrained. Strain hardening thus allows a
thermoformed skin to exhibit more evenly distributed elongation and
minimized grain washout.
[0006] One classic way to examine the strain hardening behavior of
a material is the Considre construction, by which the true stress,
defined as the force across the instantaneous cross sectional area
is plotted against the draw ratio. Regular stress-strain graphs
calculate the strain using the initial cross-sectional area, but
the cross sectional area diminishes as the sample is strained. The
Considre construction is often used to evaluate cold-drawing
phenomena.
[0007] The Considre construction can be determined by the following
equation:
.sigma..sub.T=.sigma.(1+.epsilon.)
[0008] where: .sigma..sub.T=true stress
[0009] .sigma.=engineering stress
[0010] .epsilon.=draw ratio=(L-Li)/Li
[0011] where: L=sample length under deformation
[0012] Li=initial sample length
[0013] The thermoformable compound must also exhibit acceptable
elongation characteristics at elevated temperature. If the
elongation is too low, the sheeting will tear when thermoformed.
Thus, two particularly significant tensile properties are true
ultimate tensile strength at 140.degree. C. and elongation to break
at 140.degree. C. Under extreme draw conditions of some
thermoforming applications, the Heck et al. compositions form holes
leading to part failure.
[0014] Compositions having greater melt extensibility can be
produced by lowering the level of peroxide used for rheology
modification. However, lower peroxide levels result in lower melt
strength and less tensile strength. Thus, there is a need to
produce rheology-modified TPE compositions having an improved melt
toughness. Further there is a need to enhance the high temperature
tensile properties of such compositions for thermoforming
applications.
SUMMARY OF THE INVENTION
[0015] Applicant has found that rheology modification by addition
of at least one peroxide and at least one free radical coagent has
a signicant effect on the melt toughness and high temperature
tensile properties of blends of at least one elastomeric EAO
polymer or EAO polymer blend and a polyolefin such as PP. The
rheology modified compositions of this invention have melt
toughness and high temperature tensile properties that are higher
than corresponding compositions rheology modified by the addition
of peroxides alone. As such, one aspect of this invention is a
rheology-modified, substantially gel-free thermoplastic elastomer
(TPE) composition comprising an EAO polymer or EAO polymer blend
and a high melting polymer selected from the group consisting of
polypropylene homopolymers and propylene/ethylene copolymers,
wherein the composition is rheology modified by at least one
peroxide and at least one free radical coagent and the rheology
modified composition has a melt toughness of at least 600
centinewton millimeters per second (cNmm/s), a true ultimate
tensile strength at 140.degree. C. of at least 3 mega-Pascals (MPa)
and an elongation to break at 140.degree. C. of at least 400%. The
TPE compositions may be compounded with conventional additives or
process aids including, for example, fillers, stabilizers,
dispersants, pigments and process oils. Compounds prepared from the
rheology modified polymers of this invention retain their
processing advantages over compounds prepared from the same
polymers, but rheology modified by peroxide alone.
[0016] A second aspect of this invention is a process for preparing
a rheology-modified, substantially gel-free TPE composition, the
process comprising: a) adding at least one peroxide and at least
one free radical coagent to a molten polymer blend that comprises
an elastomeric ethylene/alpha-olefin polymer and a high melting
polymer selected from the group consisting of polypropylene
homopolymers and propylene/ethylene copolymers; and b) maintaining
the polymer blend in a molten state while subjecting it to
conditions of shear sufficient to disperse the peroxide and coagent
throughout the molten polymer blend, effect rheology modification
of the polymers and substantially preclude formation of insoluble
polymer gels, sufficient rheology modification being measured by a
melt toughness of at least 600 centinewton millimeters per second
(cNmm/s), a true ultimate tensile strength at 140.degree. C. of at
least 3 mega-Pascals (MPa) and an elongation to break at
140.degree. C. of at least 400%. The process optionally includes a
step c) wherein the rheology modified polymer blend is converted to
an article of manufacture, preferably without intermediate steps of
recovering the rheology modified polymer blend as a solid and then
converting the solid to a melt state sufficient for fabricating the
article of manufacture. If desired, however, the process optionally
includes the intermediate steps.
[0017] One variation of the second aspect is a process for
preparing a rheology-modified, substantially gel-free TPE
composition, the process comprising: a) adding at least one
peroxide and at least one free radical coagent to at least one
component of a polymer blend that comprises an elastomeric
ethylene/alpha-olefin polymer and a high melting polymer selected
from the group consisting of polypropylene homopolymers and
propylene/ethylene copolymers; and b) converting the polymer blend
to a molten polymer blend while subjecting the blend to conditions
of shear sufficient to disperse the peroxide and coagent throughout
the molten polymer blend, effect rheology modification of the
polymers and substantially preclude formation of insoluble polymer
gels, sufficient rheology modification being measured by a melt
toughness of at least 600 centinewton millimeters per second
(cNmm/s), a true ultimate tensile strength at 140.degree. C. of at
least 3 mega-Pascals (MPa) and an elongation to break at
140.degree. C. of at least 400%. The process optionally includes a
sequential step c) wherein the rheology modified polymer blend is
converted to an article of manufacture, preferably without
intermediate steps of recovering the rheology modified polymer
blend as a solid and then converting the solid to a melt state
sufficient for fabricating the article of manufacture. If desired,
however, the process optionally includes the intermediate
steps.
[0018] A second variation of the second aspect is a process for
preparing a rheology-modified, substantially gel-free thermoplastic
elastomer article of manufacture, the process comprising: a) adding
at least one peroxide and at least one free radical coagent to a
molten elastomeric ethylene/alpha-olefin polymer or elastomeric
ethylene/alpha-olefin polymer blend to provide a rheology-modified
ethylene/alpha-olefin polymer or ethylene/alpha-olefin polymer
blend; b) adding to the rheology-modified polymer or polymer blend
a high melting polymer selected from the group consisting of
polypropylene homopolymers and propylene/ethylene copolymers to
form a composite polymer blend; and c) converting the composite
polymer blend into the article of manufacture, the article of
manufacture having a melt toughness of at least 600 centinewton
millimeters per second (cNmm/s), an true ultimate tensile strength
at 140.degree. C. of at least 3 mega-Pascals (MPa) and an
elongation to break at 140.degree. C. of at least 400%.
[0019] A third aspect of this invention is an article of
manufacture having at least one component thereof fabricated from
the TPE composition of the first aspect of the invention. The TPE
compositions suitably include at least one additive selected from
the group consisting of process oils, fillers and blowing agents.
The compositions readily allow formation of articles of manufacture
using apparatus for calendaring and/or thermoforming. In a related
aspect, the TPE compositions of the first aspect may be blended
with another polymer, preferably one of the polymers used to make
the TPE composition, prior to fabrication of an article of
manufacture. Such blending may occur by any of a variety of
conventional techniques, one of which is dry blending of pellets of
the TPE composition with pellets of another polymer.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0020] The rheology-modified compositions of this invention
comprise an elastomeric EAO polymer or EAO polymer blend and a high
melting polymer. The compositions desirably contain the EAO polymer
or EAO polymer blend in an amount of from about 50 to about 90 wt %
and the high melting polymer(s) in an amount of from about 50 to
about 10 wt %, both percentages being based on composition weight.
The amounts are preferably from about 65 to about 85 wt % EAO and
from about 35 to about 15 wt % high melting polymer. The amounts
are chosen to total 100 wt % polymer.
[0021] EAO polymers (also referred to as "ethylene polymers") that
are suitable for this invention include interpolymers and diene
modified interpolymers. Illustrative polymers include
ethylene/propylene (EP) copolymers, ethylene/butylene (EB)
copolymers, ethylene/octene (EO) copolymers and
ethylene/propylene/diene modified (EPDM) interpolymers. More
specific examples include ultra low linear density polyethylene
(ULDPE) (e.g., Attane.TM. made by The Dow Chemical Company),
homogeneously branched, linear EAO copolymers (e.g. Tafmer.TM. by
Mitsui PetroChemicals Company Limited and Exact.TM. by Exxon
Chemical Company), and homogeneously branched, substantially linear
EAO polymers (e.g. the Affinity.TM. polymers available from The Dow
Chemical Company and Engage.RTM. polymers available from DuPont Dow
Elastomers L.L.C. The more preferred EAO polymers are the
homogeneously branched linear and substantially linear ethylene
copolymers with a density (measured in accordance with ASTM D-792)
of from about 0.85 to about 0.92 g/cm.sup.3, especially from about
0.85 to about 0.90 g/cm.sup.3 and a melt index or 12 (measured in
accordance with ASTM D-1238 (190.degree. C./2.16 kg weight) of from
about 0.01 to about 30, preferably 0.05 to 10 g/10 min.
[0022] The substantially linear ethylene copolymers or
interpolymers (also known as "SLEPs") are especially preferred. In
addition, the various functionalized ethylene copolymers such as
EVA (containing from about 0.5 to about 50 wt % units derived from
vinyl acetate) are also suitable. When using an EVA polymer, those
that have an I.sub.2 of from about 0.01 to about 500, preferably
0.05 to 50 g/10 min are preferred.
[0023] "Substantially linear" means that a polymer has a backbone
substituted with from 0.01 to 3 long-chain branches per 1000
carbons in the backbone.
[0024] "Long-chain branching" or "LCB" means a chain length that
exceeds that of the alpha-olefin component of the EAO polymer or
EAO polymer blends. Although carbon-13 nuclear magnetic resonance
(C-13 NMR) spectroscopy cannot distinguish or determine an actual
number of carbon atoms in the chain if the length is greater than
six carbon atoms, the presence of LCB can be determined, or at
least estimated, from molecular weight distribution of the EAO
polymer(s). It can also be determined from a melt flow ratio (MFR)
or ratio (I.sub.10/I.sub.2) of melt index (I.sub.10) via ASTM
D-1238 (190.degree. C., 10 kg weight) to I.sub.2.
[0025] "Interpolymer" refers to a-polymer having polymerized
therein at least two monomers. It includes, for example,
copolymers, terpolymers and tetrapolymers. It particularly includes
a polymer prepared by polymerizing ethylene with at least one
comonomer, typically an .alpha.-olefin of 3 to 20 carbon atoms
(C.sub.3-C.sub.20). Illustrative .alpha.-olefins include propylene,
1-butene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene and
styrene. The .alpha.-olefin is desirably a C.sub.3-C.sub.10
.alpha.-olefin. Preferred copolymers include EP, EB,
ethylene/hexene-1 (EH) and EO polymers. Illustrative terpolymers
include an ethylene/propylene/octene terpolymer as well as
terpolymers of ethylene, a C.sub.3-C.sub.20 .alpha.-olefin and a
diene such as dicyclopentadiene, 1,4-hexadiene, piperylene or
5-ethylidene-2-norbornene.
[0026] "Elastomeric", as used herein, means an EAO polymer or EAO
polymer blend that has a density that is beneficially less than
about 0.920 g/cc, desirably less than about 0.900 g/cc, preferably
less than about 0.895 g/cc, more preferably less than about 0.880
g/cc, still more preferably less than about 0.875 g/cc, even more
preferably less than about 0.870 g/cc and a percent crystallinity
of less than about 33%, preferably less than about 29% and more
preferably less than about 23%. The density is preferably greater
than about 0.850 g/cc. Percent crystallinity is determined by
differential scanning calorimetry (DSC).
[0027] SLEPs are characterized by narrow molecular weight
distribution (MWD) and narrow short chain branching distribution
(SCBD) and may be prepared as described in U.S. Pat. Nos. (USP)
5,272,236 and 5,278,272, relevant portions of both being
incorporated herein by reference. The SLEPs exhibit outstanding
physical properties by virtue of their narrow MWD and narrow SCBD
coupled with long chain branching (LCB).
[0028] U.S. Pat. No. 5,272,236 (column 5, line 67 through column 6,
line 28) describes SLEP production via a continuous controlled
polymerization process using at least one reactor, but allows for
multiple reactors, at a polymerization temperature and pressure
sufficient to produce a SLEP having desired properties.
Polymerization preferably occurs via a solution polymerization
process at a temperature of from 20.degree. C. to 250.degree. C.,
using constrained geometry catalyst technology. Suitable
constrained geometry catalysts are disclosed at column 6, line 29
through column 13, line 50 of U.S. Pat. No. 5,272,236.
[0029] A preferred SLEP has a number of distinct characteristics,
one of which is an ethylene content that is between 20 and 90 wt %,
more preferably between 30 and 89 wt %, with the balance comprising
one or more comonomers. The ethylene and comonomer contents are
based on SLEP weight and selected to attain a total monomer content
of 100 wt %. For chain lengths up to six carbon atoms, SLEP
comonomer content can be measured using C-13 NMR spectroscopy.
[0030] Additional distinct SLEP characteristics include I.sub.2 and
MFR or I.sub.10/I.sub.2. The interpolymers desirably have an
I.sub.2 of 0.01-30 g/10 min, more preferably from 0.05-10 g/10 min.
The SLEP also has a I.sub.10/I.sub.2 (ASTM D-1238).gtoreq.5.63,
preferably from 6.5 to 15, more preferably from 7 to 10. For a
SLEP, the I.sub.10/I.sub.2 ratio serves as an indication of the
degree of LCB such that a larger I.sub.10/I.sub.2 ratio equates to
a higher degree of LCB in the polymer.
[0031] SLEPs that meet the aforementioned criteria include, for
example, Engage.RTM. polyolefin elastomers and other polymers
produced via constrained geometry catalysis by The Dow Chemical
Company and DuPont Dow Elastomers L.L.C.
[0032] The high melting polymer component of the TPEs of this
invention is a homopolymer of propylene or a copolymer of propylene
with an .alpha.-olefin such as ethylene, 1-butene, 1-hexene or
4-methyl-1-pentene or a blend of a homopolymer and a copolymer.
Each of the homopolymer, the copolymer or the blend of a
homopolymer and a copolymer may be nucleated. The .alpha.-olefin is
preferably ethylene. The copolymer may be a random copolymer or a
block copolymer or a blend of a random copolymer and a block
copolymer. As such, this component is preferably selected from the
group consisting of polypropylene (PP) homopolymers and
propylene/ethylene copolymers. This component has a MFR
(230.degree. C. and 2.16 kg weight) of 0.3 to 60 g/10 min,
preferably 0.8 to 40 g/10 min and more preferably 1 to 35 g/10
min.
[0033] As used herein, "nucleated" refers to a polymer that has
been modified by addition of a nucleating agent such as Millad.TM.,
a dibenzyl sorbitol commercially available from Milliken. Other
conventional nucleating agents may also be used.
[0034] Preparation of polypropylene (PP) also involves the use of
Ziegler catalysts such as a titanium trichloride in combination
with aluminum diethylmonochloride, as described by Cecchin, U.S.
Pat. No. 4,177,160. Polymerization processes used to produce PP
include the slurry process, which is run at about 50-90.degree. C.
and 0.5-1.5 MPa (5-15 atm), and both the gas-phase and
liquid-monomer processes in which extra care must be given to the
removal of amorphous polymer. Ethylene may be added to the reaction
to form a polypropylene with ethylene blocks. PP resins may also be
prepared by using any of a variety of metallocene, single site and
constrained geometry catalysts together with their associated
processes.
[0035] The peroxide is preferably an organic peroxide. Suitable
organic peroxides have a half life of at least one hour at
120.degree. C. Illustrative peroxides include a series of
vulcanizing and polymerization agents that contain
.alpha.,.alpha.'-bis(t-butylperoxy)-diisopropylbenzen- e and are
available from Hercules, Inc. under the trade designation
VULCUP.TM., a series of such agents that contain dicumyl peroxide
and are available from Hercules, Inc. under the trade designation
Di-cup.TM. as well as Lupersol.TM. peroxides made by Elf Atochem,
North America or Trigonox.TM. organic peroxides made by Akzo Nobel.
The Lupersol.TM. peroxides include Lupersol.TM. 101
(2,5-dimethyl-2,5-di(t-butylperoxy)hex- ane), Lupersol.TM. 130
(2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3) and Lupersol.TM.575
(t-amyl peroxy-2-ethylhexonate). Other suitable peroxides include
2,5-dimethyl-2,5-di-(t-butyl peroxy)hexane, di-t-butylperoxide,
di-(t-amyl)peroxide, 2,5-di(t-amyl peroxy)-2,5-dimethylhexane,
2,5-di-(t-butylperoxy)-2,5-diphenylhexane,
bis(alpha-methylbenzyl)peroxid- e, benzoyl peroxide, t-butyl
perbenzoate, 3,6,9-triethyl-3,6,9-trimethyl-1- ,4,7-triperoxonane
and bis(t-butylperoxy)-diisopropylbenzene.
[0036] The peroxide is suitably present in an amount that is within
a range of from about 100 to about 10,000 parts by weight per
million parts by weight of polymer. The range is desirably from
about 500 to about 5,000, preferably from about 1,000 to about
3,000 parts by weight.
[0037] The free radical coagent is a monomer or low molecular
weight polymer having two or more functional groups with high
response to free radicals. Typically, these functional groups are
either methacrylate, allyl or vinyl. The free radical coagent
enhances the rheology modification of the peroxide by two
mechanisms. Firstly, by peroxide induced allylic hydrogen
abstraction from the coagent, a lower energy state, longer lived
free radical is created. This free radical can then induce
branching in the ethylene elastomer by hydrogen abstraction. Due to
the lower energy state of the free radical, (.beta.-scissioning and
disproportionation of either the polypropylene or ethylene
elastomer phase is less likely to occur. Secondly, the
multifunctional coagent can act as a bridging group between the
polymer chains.
[0038] Suitable free radical coagents for this application would
include diallyl terephthalate, triallylcyanurate,
triallylisocyanurate, 1,2 polybutadiene, divinyl benzene,
trimethylolpropane trimethacrylate, polyethylene glycol
dimethacrylate, ethylene glycol dimethacrylate, pentaerythritol
triacrylate,allyl methacrylate, N N'-m-phenylene bismaleimide,
toluene bismaleimide-p-quinone dioxime, nitrobenzene,
diphenylguanidine. Preferred coagents are triallylcyanurate, 1,2
polybutadiene, divinyl benzene, and trimethyolpropane
trimethacrylate.
[0039] The coagent is suitably present in an amount that is within
the range of from about 100 to about 10,000 parts per million by
weight. The range is desirably from about 500 to about 5,000 parts,
preferrably from 1,000 to 3,000 parts per million by weight.
[0040] The peroxide and free radical coagent can be added by any
conventional means. Illustrative procedures include imbibing it
onto polymer pellets prior to compounding, adding it to polymer
pellets as the pellets enter a compounding apparatus such as at the
throat of an extruder, adding it to a polymer melt in a compounding
apparatus such as a Haake, a Banbury mixer, a Farrel continuous
mixer or a Buss kneader or injecting it into an extruder, at 100%
active ingredients (i.e., neat) or optionally as a dispersion or
solution in an oil, such as a processing oil, at a point where the
extruder contents are molten. A preferred procedure is imbibing the
peroxide and coagent into the polymer pellets prior to
compounding.
[0041] The peroxide and free radical coagent are used in amounts
sufficient to provide a melt toughness of at least 600 centinewton
millimeters per second (cNmm/s), a true ultimate tensile strength
at 140.degree. C. of at least 3 mega-Pascals (MPa) and an
elongation to break at 140.degree. C. of at least 400% without
substantial gel formation. The ratio of coagent to peroxide is
suitably within the range from about 1:10 to 10:1 based on wt. %. A
more preferred ratio range is from about 1:5 to 5:1 and the most
preferred ratio range is from about 1:2 to about 2:1. The optimum
ratio of coagent is dependent on the
ethylene/.quadrature.-olefin-polypropylene ratio used in the
compounds. A suitable range of EAO/PP on a weight percent basis is
80/20-40/60. The preferred range is 65/35-75/25 weight percent.
[0042] Melt toughness, as used herein, is the product of the melt
strength and melt extensibility. Melt strength (MS), as used
herein, is a maximum tensile force measured on a molten filament of
a polymer melt extruded from a capillary rheometer die at a
constant shear rate of 33 reciprocal seconds (sec-1) while the
filament is being stretched by a pair of nip rollers that are
accelerating the filament at a rate of 0.24 centimeters per second
per second (cm/sec.sup.2) from an initial speed of 1 cm/sec. The
molten filament is preferably generated by heating 10 grams (g) of
a polymer that is packed into a barrel of an Instron capillary
rheometer, equilibrating the polymer at 190.degree. C. for five
minutes and then extruding the polymer at a piston speed of 2.54
cm/minute (cm/min) through a capillary die with a diameter of 0.21
cm and a length of 4.19 cm. The tensile force is preferably
measured with a Goettfert Rheotens that is located so that the nip
rollers are 10 cm directly below a point at which the filament
exits the capillary die. Melt extensibility (ME), as used herein,
is the maximum speed of the nip rollers from the Goettfert Rheotens
needed to break the filament, measured in cm/sec.
[0043] The high temperature ultimate tensile strength or ultimate
tensile strength at 140.degree. C., as used herein, is measured by
cutting ISO 37 T2 dumbbell bars from either the compression molded
plaque or extruded sheet. When testing extruded sheet, the bars are
cut in the machine direction. The cut bar is then placed in a
tensile testing machine fitted with an environmental chamber heated
to 140.degree. C. The bar is allowed to equilibrate for 10 minutes,
then is strained at a cross head speed of 50 cm/min. The tensile
strength and elongation to break are recorded.
[0044] In order to detect the presence of, and where desirable,
quantify insoluble gels in a polymer composition such as the
rheology-modified compositions of this invention, simply soak the
composition in a suitable solvent such as refluxing xylene for 12
hours as described in ASTM D 2765-90, method B. Any insoluble
portion of the composition is then isolated, dried and weighed,
making suitable corrections based upon knowledge of the
composition. For example, the weight of non-polymeric components
that are soluble in the solvent is subtracted from the initial
weight and the weight of non-polymeric components that are
insoluble in the solvent is subtracted from both the initial and
final weight. The insoluble polymer recovered is reported as
percent gel content. For purposes of this invention, "substantially
gel-free" means a percent gel content that is desirably less than
about 10%, more desirably less than about 8%, preferably less than
about 5%, more preferably less than about 3%, still more preferably
less than about 2%, even more preferably less than about 0.5% and
most preferably below detectable limits when using xylene as the
solvent. For certain end use applications where gels can be
tolerated, the percent gel content can be higher.
[0045] The compositions of this invention may be compounded with
any one or more materials conventionally added to polymers. These
materials include, for example, EAOs that have not been rheology
modified, process oils, plasticizers, specialty additives including
stabilizers, fillers (both reinforcing and non-reinforcing) and
pigments. These materials may be compounded with compositions of
this invention either before or after such compositions are
rheology modified. Skilled artisans can readily select any suitable
combination of additives and additive amounts as well as timing of
compounding without undue experimentation.
[0046] Process oils are often used to reduce any one or more of
viscosity, hardness, modulus and cost of a composition. The most
common process oils have particular ASTM designations depending
upon whether they are classified as paraffinic, naphthenic or
aromatic oils. An artisan skilled in the processing of elastomers
in general and the rheology-modified TPE compositions of this
invention in particular will recognize which type of oil will be
most beneficial. The process oils, when used, are desirably present
in an amount within a range of from about 0.5 to about 50 wt %,
based on total composition weight. Certain low to medium molecular
weight ester plasticizers may also used to enhance low temperature
performance. Examples of esters which may be used include
isooctyltallate, isooctyloleate, n-butyltallate, n-butyloleate,
butoxyethyloleate, dioctylsebacate, di2-ethyle hexylsebacate,
dioctylazelate, diisooctyldodecanedioate, alkylalkylether diester
glutarate.
[0047] A variety of specialty additives may be advantageously used
in compositions of this invention. The additives include
antioxidants, surface tension modifiers, anti-block agents,
lubricants, antimicrobial agents such as organometallics,
isothtazolones, organosulfurs and mercaptans; antioxidants such as
phenolics, secondary amines, phophites and thioesters; antistatic
agents such as quaternary ammonium compounds, amines, and
ethoxylated, propoxylated or glycerol compounds; fillers and
reinforcing agents such as carbon black, glass, metal carbonates
such as calcium carbonate, metal sulfates such as calcium sulfate,
talc, clay or graphite fibers; hydrolytic stabilizers; lubricants
such as fatty acids, fatty alcohols, esters, fatty amides, metallic
stearates, paraffinic and microcrystalline waxes, silicones and
orthophosphoric acid esters; mold release agents such as
fine-particle or powdered solids, soaps, waxes, silicones,
polyglycols and complex esters such as trimethylolpropane
tristearate or pentaerythritol tetrastearate; pigments, dyes and
colorants; plasticizers such as esters of dibasic acids (or their
anhydrides) with monohydric alcohols such as o-phthalates, adipates
and benzoates; heat stabilizers such as organotin mercaptides, an
octyl ester of thioglycolic acid and a barium or cadmium
carboxylate; ultraviolet light stabilizers used as a hindered
amine, an o-hydroxy-phenylbenzotriaz- ole, a
2-hydroxy,4-alkoxyenzophenone, a salicylate, a cynoacrylate, a
nickel chelate and a benzylidene malonate and oxalanilide. A
preferred hindered phenolic antioxidant is Irganox.TM. 1076
antioxidant, available from Ciba-Geigy Corp. Each of the above
additives, if used, typically does not exceed 45 wt %, based on
total composition weight, and are advantageously from about 0.001
to about 20 wt %, preferably from about 0.01 to about 15 wt % and
more preferably from about 0.1 to about 10 wt %.
[0048] The rheology-modified TPE compositions of this invention may
be fabricated into parts, sheets or other form using any one of a
number of conventional procedures for processing TPEs. The
compositions can also be formed, spun or drawn into films, fibers,
multi-layer laminates or extruded sheets, or can be compounded with
one or more organic or inorganic substances, on any machine
suitable for such purposes. The compositions are particularly
advantageous for high temperature TPE processes such as
calendaring, extruding and thermoforming.
[0049] The TPE compositions of this invention have surprisingly
improved properties relative to blends of an EAO copolymer and a
high melting polymer such as PP that have been subjected to
rheology modification by peroxide only. Rheology modification by
way of peroxide and free radical coagent provides a combination of
desirable and improved melt toughness and high temperature tensile
properties.
[0050] The compositions of this invention can be formed into a
variety of shaped articles using conventional polymer fabrication
processes such as those identified above. A partial, far from
exhaustive, listing of suitable shaped articles includes automobile
body parts such as instrument panel skins, bumper fascia, body side
moldings, exterior trim, interior trim,weather stripping, air dams,
air ducts, and wheel covers, and non-automotive applications such
as polymer films, polymer sheets, tubing, trash cans, storage
containers, lawn furniture strips or webbing, lawn mower, garden
hose, and other garden appliance parts, recreational vehicle parts,
golf cart parts, utility cart parts and water craft parts. The
compositions can also be used in roofing applications such as
roofing membranes. The compositions can further be used in
fabricating components of footwear such as a shaft for a boot,
particularly an industrial work boot. A skilled artisan can readily
augment this list without undue experimentation.
[0051] The following examples illustrate but do not, either
explicitly or by implication, limit the present invention. Unless
otherwise stated, all parts and percentages are by weight, on a
total weight basis. Examples of the present invention are
identified by Arabic numerals and comparative examples are
represented by letters of the alphabet.
EXAMPLES AND COMPARATIVE EXAMPLE
[0052] Nine compositions, eight representing this invention
(Examples 1-8) and one being a comparison (Comparative Example A),
were prepared from two different EAO polymers using the following
procedure. All nine compositions were produced by tumble blending
the ingredients together, allowing the peroxide and coagent to
imbibe into the pellets, then processing the blend into pellets on
a Werner Pfliederer ZSK-30 co-rotating twin screw extruder. The
pelletized compounds were then processed into sheeting on a 2 inch
Killion single screw extruder fitted with a 6 inch wide sheeting
die. Sheeting 0.050 inch thick was produced and tested.
[0053] The EAO polymers used in the examples were: EAO-1, an
ethylene/1 -octene copolymer having an I.sub.2 of 0.5 g/10 min and
a nominal density of 0.863 g/cc (Engage.RTM. 8180 polyolefin
elastomer from DuPont Dow Elastomers L.L.C.); EAO-2, an
experimental ethylene/1-octene copolymer having a nominal Mooney
viscosity of 47, a nominal density of 0.868 g/cc, a number average
molecular weight of about 80,000 and a molecular weight
distribution (MWD) of about 2.3, as measured by gel permeation
chromatography (produced by DuPont Dow Elastomers L.L.C.); and
EAO-3, an experimental ethylene/1-butene copolymer having a nominal
Mooney viscosity of 45, a nominal density of 0.870 g/cc, a number
average molecular weight (Mn) of about 78,000, and a molecular
weight distribution (MWD) of about 2.0 as measured by gel
permeation chromatography (produced by DuPont Dow Elastomers
L.L.C.).
[0054] The polypropylene (PP) used in the examples was a
polypropylene homopolymer having a melt flow of 0.8 (Profax PD-191
from Montell).
[0055] The peroxides used in the examples were:
POX-1,2,5-dimethyl-2,5-di(- t-butylperoxy)hexane (Lupersol 101 from
Elf Atochem); and POX-2, di(t-amyl)peroxide (DTAP from Crompton
Chemical).
[0056] The free radical coagents used in the examples were: FRC-1,
trimethylolpropane trimethacrylate (SR-350 KD96 (75% SR-350 from
Sartomer Company, Inc. on calcium silicate prepared by Akron
Dispersions)); FRC-2, trimethylolpropane trimethacrylate (100%
SR-350 from Sartomer Company,Inc.); FRC-3, triallyl cyanurate (TAC
from Cytec Industries, Inc.); and FRC-4, 1,2-polybutadiene (Ricon
152D (68% Ricon 152 from Sartomer Coporation on calcium silicate,
prepared by Akron Dispersions)). FRC-4 was warmed to about
30.degree. C. to form a liquid prior to tumble blending.
Examples 1-2 and Comparative Example A
[0057] Table I summarizes data for the compositions of Examples 1-2
and Comparative Example A. Table I identifies the EAO polymer, the
peroxide and the free radical coagent (for Examples 1 and 2), and
specifies the wt % of the ingredients.
1TABLE I Example EAO-1 PP POX-1 FRC-1 1 68.7 30.8 0.2 0.3 2 68.6
30.7 0.3 0.4 A 68.6 30.7 0.7 0
[0058] The properties of the compositions of the examples and
comparative example were determined and are reported in Table II
below.
[0059] A Goeffert Rheotens measured the melt strength (MS) and melt
extensibility (ME) of a molten filament of a polymer melt extruded
from a capillary rheometer die. Melt toughness (MT) is the product
of the MS and the ME. A constant shear rate of 33 sec.sup.-1 was
maintained while the filament was being stretched by a pair of nip
rollers that were accelerating the filament at a rate of 0.24
cm/sec.sup.2 from an initial speed of 1 cm/sec. The nip rollers
were fitted with strain gages to measure the stress response of the
molten filament to strain. Elevated temperature (140.degree. C.)
stress strain was measured with a tensile testing machine fitted
with an environmental chamber heated to 140.degree. C. The true
stress (true ultimate tensile strength (TUTS)) was determined using
the Considere equation and the elongation to break (ultimate strain
(US)) was measured. Gel content of the composition was measured by
extracting with refluxing xylene for 12 hours as described in ASTM
D 2765-90.
2TABLE II 140.degree. C. 140.degree. C. MS ME MT TUTS US Gel
Example (cN) (mm/s) (cNmm/s) (Mpa) (%) (wt %) 1 10.58 115.6 1223
0.480 >1200 0.9 2 17.36 78.1 1356 0.905 523 0.6 A 7.55 75.3 569
0.457 344 1.0
[0060] The data presented in Table II illustrate several points.
First, Examples 1 and 2 show significantly higher melt toughness
than Comparative Example A. These results evidence that higher melt
toughness is obtained using a lower level of peroxide with a free
radical coagent. Second, Examples 1 and 2 show greater tensile
properties at the high temperature of 140.degree. C. Example 1 has
a slightly higher true ultimate tensile strength and a
significantly higher ultimate stress than Comparative Example A.
Example 2 has nearly twice the true ultimate tensile strength and
significantly higher ultimate stress than Comparative Example A.
Similar results are expected with other EAO polymers, propylene
polymers, and rheology modifiers or modification processes, all of
which are disclosed above.
Examples 3-8
[0061] Using different EAO polymers, peroxides and/or free radical
coagents, the procedure and apparatus of Examples 1-2 were used to
prepare six additional compositions of the invention. Table III
identifies the EAO polymer, the peroxide and the free radical
coagent, and specifies the wt % of the ingredients.
3TABLE III Ex. EAO-1 EAO-2 EAO-3 PP POX-1 POX-2 FRC-2 FRC-3 FRC-4 3
69.79 0 0 29.91 0 0.15 0.15 0 0 4 69.79 0 0 29.91 0.15 0 0 0.15 0 5
0 69.79 0 29.91 0.15 0 0.15 0 0 6 0 69.79 0 29.91 0.05 0 0.05 0 0 7
0 0 69.79 29.91 0.15 0 0.15 0 0 8 69.7585 0 0 29.8965 0.15 0 0 0
0.195
[0062] Table IV The properties of the compositions of Examples 3-8
were determined in the same manner as described above for Examples
1-2 and Comparative Example A. They are reported in Table IV
below.
4 140.degree. C. 140.degree. C. MS ME MT TUTS US Gel Example (cN)
(mm/s) (cNmm/s) (Mpa) (%) (wt %) 3 27 43 1161 5.25 1367 0.9 4 25 61
1525 5.09 1287 1.4 5 27 45.9 1239 4.26 1510 1.1 6 13 82.6 1074 7.71
1300 0.9 7 21 65.3 1371 11.7 1324 0.16 8 21 55.4 1163 9.6 1364
0.30
[0063] Examples 3-8 show much higher melt toughness (1074-1525
cN-mm/s) than Comparative Example A (569 cN-mm/s). Further,
Examples 3-8 show much higher true ultimate tensile strength at
140.degree. C. and significantly higher ultimate strain at
140.degree. C. than Comparative Example A. Similar results are
expected with other EAO polymers and blends of EAO polymers, PP
polymers, peroxides, free radical coagents or procedures and
amounts of the same, all of which are disclosed herein.
* * * * *