Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CONSTRUCTION COMPRISING TIE LAYER
FIELD OF THE INVENTION
[0002] This invention relates to compositions useful in
multilayer constructions, for example in tire construction,
especially a tire tie layer between an innerliner and
carcass. In particular, this invention relates to rubber
compositions utilizing halogenated isobutylene-containing
elastomers, optionally in blends with high diene-containing
elastomer or rubber, such as natural rubber (NR) and
styrene butadiene rubber (SBR).
=
BACKGROUND OF THE INVENTION
[0003] To prevent tire cord strike-through, a condition
wherein the reinforcing tire cord penetrates the innerliner
layer, leading to air leakage and tire failure, it is a
common practice to add a buffer layer between the carcass
layer containing textile or steel cords and the innerliner
layer. This buffer layer has been referred to as tie gum,
tie layer, cushion compound, or liner backing layer and
typically includes blends of natural rubber (NR) and
styrene-butadiene rubber (SBR). For purposes of the
present invention, this tire component is referred to as
the "tie layer." Typically, the composition of the tie
layer is similar to the composition of the carcass compound
in order to provide the necessary building tack for
maintaining a coherent tire structure in the uncured, or
"green," state, cured adhesion, and satisfactory dynamic
properties during tire use. However, both NR and SBR are
highly permeable rubbers. Consequently, a thicker cross-
section would be
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required in order to reduce air permeability though this
layer and so maintain tire pressure. In order to achieve
overall weight reduction in a tire by using a thin,
highly impermeable innerliner, it is necessary to find a
means of reducing the cross-sectional thickness of the
tie layer.
[0004] U.S. Pat. No. 5,738,158 discloses a pneumatic
tire having an air permeation prevention layer or
innerliner layer composed of a thin film of a resin
composition including at least 20-, by weight of a
thermoplastic polyester elastomer comprised of a block
copolymer of polybutylene terephthalate and
polyoxyalkylene diimide diacid at a weight ratio of
polybutylene terephthalate/polyoxyalkylene diimide diacid
of 85/15 or less. The resin composition can further
include dispersed rubber particles wherein the rubber
particles have been dynamically vulcanized. The concept
of using a resin composition as an innerliner layer has
been further developed by various Inventors of the same
assignee, see, e.g., U.S. Pat. No. 6,079,465, which
claims a pneumatic tire that incorporates such an
innerliner and discloses the use of various thermoplastic
resins for use in the composition. This patent also
discloses the presence of a tie layer and another layer
to promote bond or adhesive strength of the innerliner
layer in the overall structure. The further development
of this technology to improve adhesion of the innerliner
layer in the structure is described in U.S. Pat. No.
6,062,283 wherein melt viscosities and solubility
parameters of thermoplastic resin components and
elastomer components are controlled according to a
specific mathematical formula.
[0005] Published application U.S. 2002/0066512
discloses a pneumatic tire comprising a carcass
comprising a ply of cords defining the innermost
reinforcing cord layer extending between bead portions,
and an airtight layer disposed inside the cords of the
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carcass ply along the inner surface of the tire, covering
the substantially entire inner surface of the tire,
wherein the airtight layer is made of air-impermeable
rubber including at least 10 weight 96 of halogenated
butyl rubber and/or halogenated isobutylene-paramethyl
styrene copolymer in its rubber base, and a thickness of
the airtight layer measured from the inner surface of the
tire to the cords of the carcass ply is in a range of
from 0.2 to 0.7 mm. The publication also discloses that
the "airtight layer," defined by a rubber layer between
the tire inner surface and the innermost tire cords or
carcass cords, can be a double layer comprising an inner
layer of an air-impermeable rubber compound and an outer
layer of a diene-based rubber which is not air-
impermeable.
[0006] Alternatively, the outer layer may be of the
same air-impermeable rubber compound or a similar air-
impermeable rubber compound, which compound is further
described in the publication as including halogenated
butyl rubber and/or halogenated isobutylene-paramethyl
styrene copolymer and diene rubber as well as carbon
black (see paragraphs 28-34).
[0007] Other references of interest include: WO
2004/081107, WO 2004/081106, WO 2004/081108, WO
2004/081116, WO 2004/081099, JP 2000238188, EP 01 424
219, U.S. Pat. No. 6,759,136, and U.S. Pat. No.
6,079,465.
SUMMARY OF THE INVENTION
[0008] The present invention provides a solution by
using at least one highly impermeable isobutylene-based
elastomer in the tie layer; particularly preferred
impermeable elastomers being brominated isobutylene-
isoprene copolymers (BIIR), i.e., bromobutyl copolymer.
The present invention is useful in tires employing
thermoplastic elastomeric tire innerliner compositions
based on vulcanized blends of engineering resins, e.g.,
polyamides and BIMS, produced, for example, using dynamic
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vulcanization. The tie layer is directly adhered to the
dynamically vulcanized alloy layer without impairing the
improved permeability characteristics achieved by the
innerliner and without using additional bonding means to
secure the two layers together.
[0009] One aspect of the disclosed invention is a
process for forming a layered structure wherein a fluid
permeation prevention film and an adhesive tie layer are
directly bonded together. Prior to bonding the two
layers, the fluid permeation prevention layer is treated
to remove any residual plasticizers or oils on the
surface of the film. The two layers of the layered
structure may be separately extruded and then adhered to
each other or adhered to each other during a calendering
operation wherein the adhesive tie layer composition is
coated onto the treated film.
[0010] In any aspect of the disclosed invention, the
tie layer comprises a mixture of 100 weight % of at least
one halogenated isobutylene containing elastomer and
about 1 to about 20 parts per hundred (phr) of at least
one tackifier.
[0011] In any aspect of the disclosed invention, the
fluid permeation prevention film comprises an elastomeric
component dispersed in a vulcanized or partially
vulcanized state, as a discontinuous phase, in a matrix
of the thermoplastic resin component.
[0012] The present invention is also useful in other
applications in which an air or fluid holding layer is
used in combination with another layer, particularly
where the other layer includes reinforcing fibers or
cords, e.g., hoses and other vessels required to retain a
gas or a fluid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic diagram of a multi-zone
oven for treating the DVA film to remove the residual
plasticizer;
[0014] FIG. 2 is an exemplary calendering system for
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application of the adhesive tie gum layer; and
[0015] FIG. 3 is a simplified cross-sectional view of
a tire showing the location of various layers in a tire
including a tie layer.
DETAILED DESCRIPTION
[0016] The present invention relates to a rubber
composition for a relatively impermeable tie layer
between innerliner and carcass for tire weight reduction
while maintaining the heat resistance, durability, and
flexibility demanded for a pneumatic tire. The present
invention is also directed to reducing the permeability
of the tie layer with improved durability while achieving
excellent adhesion to both the carcass and innerliner.
[0017] Polymer may be used to refer to homopolymers,
copolymers, interpolymers, terpolymers, etc. Likewise, a
copolymer may refer to a polymer comprising at least two
monomers, optionally with other monomers. When a polymer
is referred to as comprising a monomer, the monomer is
present in the polymer in the polymerized form of the
monomer or in the derivative form the monomer. However,
for ease of reference the phrase "comprising the
(respective) monomer" or the like is used as shorthand.
Likewise, when catalyst components are described as
comprising neutral stable forms of the components, it is
well understood by one skilled in the art, that the
active form of the component is the form that reacts with
the monomers to produce polymers.
[0018] Isoolefin refers to any olefin monomer having
two substitutions on the same carbon. Multiolefin refers
to any monomer having two or more double bonds. In a
preferred embodiment, the multiolefin is any monomer
comprising two double bonds, preferably two conjugated
double bonds such as a conjugated diene like isoprene.
[0019] Elastomer(s) as used herein, refers to any
polymer or composition of polymers consistent with the
ASTM D1566-06 definition. The terms may be used
interchangeably with the term "rubber(s)."
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[0020] The present invention is directed to a layered
construction having one layer comprising an thermoplastic
engineering resin (also called an "engineering resin" or
a "thermoplastic resin") as a continuous phase and a
vulcanized (or partially vulcanized) elastomer as a
dispersed phase. Such a composition is prepared, for
example, by utilizing technology known as dynamic
vulcanization and the resulting composition is known as a
dynamically vulcanized alloy (DVA); details of such a
composition and its method of preparation are described
herein. In the context of its use in pneumatic tires,
the DVA layer serves as a tire innerliner. In general,
this layer will be referred as the air permeation
prevention layer or barrier layer since this is the layer
with the lowest permeation rate.
[0021] Adjacent to the air permeation prevention layer
is an adhesive tie layer, so named because it ties the
DVA innerliner to the adjacent layers in the constructed
tire - typically, the adjacent layer will be the radially
innermost surface of the carcass and the radially
innermost coating rubber of the carcass layer. The tie
layer is preferably a vulcanizable composition, typically
containing at least one reinforcing filler as well as
optional additives such as processing aids, etc., and,
for purposes of the present invention, the tie layer
comprises a halogenated isobutylene-containing elastomer.
[0022] In accordance with the present, by formulation
and/or treatment of the air permeation prevention layer,
the adhesive tie lay may be bonded directly to the air
permeation prevention layer without requiring the use of
intermediate adhesive layers between the two layers.
Fluid Permeation Prevention Layer
[0023] The fluid permeation prevention layer is
typically present in the form of a sheet or a film for
tire constructions, but may also be present in the form
of a tubular layer of a hose construction. The sheet or
film may be extruded as a blown sheet or tubular layer or
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cast into a film. Either method of forming the layer may
result in a layer of consistent thickness or a varying
thickness as desired to achieve greater thicknesses in
different areas corresponding to the various areas of
flexibility of the article in which it is to used.
[0024] The fluid permeation prevention layer, as noted
is formed from a DVA having a vulcanized, or partially
vulcanized, elastomer dispersed as discrete particles
within a continuous phase of thermoplastic engineering
resin.
Elastomer
[0025] The elastomers useful in the DVA of the
invention are any C4 to C7 alkene monomer derived
elastomer. One such elastomer useful in the invention is
a typically prepared by reacting a mixture of monomers,
the mixture having at least (1) a C4 to C7 alkene monomer
with (2) at least one multiolefin, monomer component.
The alkene is in a range from 70 to 99. 5 wt % by weight
of the total monomer mixture in one embodiment, and 85 to
99. 5 wt % in another embodiment. The alkene is a C, to
C7 compound, non-limiting examples of which are compounds
such as isobutylene, 2-methyl-l-butene, 3-methyl-l-
butene, 2-methyl-2-butene, 1-butene, 2-butene, hexene,
and 4-methyl-1-pentene. A preferred alkene for the
invention is a C4 to C7 isoolefin or alternatively a C4
to C7 isomonoolefin. A useful monomer is isobutylene
resulting in isobutylene-based polymers. The multiolefin
component is present in the monomer mixture from 30 to
0.5 wt % in one embodiment, and from 15 to 0.5 wt % in
another embodiment. In yet another embodiment, from 8 to
0.5 wt % of the monomer mixture is multiolefin. The
multiolefin is a C4 to C14 multiolefin such as isoprene,
butadiene, 2,3-dimethy1-1,3-butadiene, myrcene, 6,6-
dimethyl-fulvene, hexadiene, cyclopentadiene, and
piperylene. Useful in the invention is an elastomer
obtained by reacting 92 to 99.5 wt I of isobutylene with
0.5 to 8 wt I isoprene, or reacting 99.5 wt% to 95 wt%
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isobutylene with 0.5 wt % to 5.0 wt % isoprene; this
isobutylene-isoprene copolymer (IIR) is conventionally
referred to as butyl rubber/elastomer.
[0026] It is useful in the invention to use a
halogenated rubber. Halogenated rubber is conventionally
defined as a rubber having at least about 0. 1 mole %
halogen based on total moles of monomers and co-monomers,
such halogen selected from the group consisting of
bromine, chlorine and iodine. Halogenated rubbers useful
in this invention include halogenated isobutylene
containing elastomers (also referred to as halogenated
isobutylene-based copolymers). These elastomers can be
described as random copolymers of a C4 to C7 isomonoolefin
derived unit, such as isobutylene derived unit, and at
least one other polymerizable unit. In one embodiment of
the invention, the halogenated isobutylene-containing
elastomer is a butyl-type rubber or branched butyl-type
rubber, especially brominated versions of these
elastomers. Preferred halogenated isobutylene-based
homopolymers or copolymers useful in this invention
include halobutyl rubbers, such as bromobutyl rubber and
chlorobutyl rubber.
[0027] Halogenated butyl rubber is produced by the
halogenation of the butyl rubber product described above.
Halogenation can be carried out by any means, and the
invention is not herein limited by the halogenation
process. Methods of halogenating polymers such as butyl
polymers are disclosed in U.S. Pat. Nos. 3,099,644,
4,513,116, and 5,681,901. In a conventional process,
butyl rubber is halogenated in hexane diluent at from 4
to 60 C using bromine (Br2) or chlorine (C12) as the
halogenation agent. The halogenated butyl rubber
typically has a Mooney Viscosity of about 27 to about 51
(ML 1+8 at 125 C). The halogen content is typically
about 0.1 to 10 wt % based on the weight of the
halogenated butyl rubber; for example, about 0.5 to 5 wt
%; alternatively, about 0.8 to about 2.5 wt %; for
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example, about 1 to about 2 wt %. A commercial
embodiment of a halogenated isobutylene containing
elastomer useful in the present invention is Bromobutyl
2222 (ExxonMobil Chemical Company). Its Mooney Viscosity
is typically about 27 to 37 (ML 1+8 at 125 C. , ASTM
D1646-04, modified), and its bromine content is about 1.8
to 2.2 wt % relative to the halogenated elastomer.
Furthermore, the cure characteristics of Bromobutyl 2222
as provided by the manufacturer are as follows: MH about
28 to 40 dN m, ML is about 7 to 18 dN m (ASTM D2084-92A).
Another commercial embodiment of a halogenated
isobutylene containing elastomer useful in the present
invention is Bromobutyl 2255 (ExxonMobil Chemical
Company). Its Mooney Viscosity is about 41 to 51 (ML 1+8
at 125 C., ASTM D1646-04), and its bromine content is
about 1. 8 to 2. 2 wt %. Furthermore, its cure
characteristics as disclosed by the manufacturer are as
follows: MH is from 34 to 48 dN m, ML is from 11 to 21 dN
m (ASTM D2084-92A).
[0028] Another useful embodiment of halogenated
isobutylene containing elastomer is halogenated, branched
or "star-branched" butyl rubber. In one embodiment, the
star-branched butyl rubber ("SBB") is a composition
comprising butyl rubber and a polydiene or block
copolymer. For purposes of the present invention, the
method of forming the SBB is not a limitation. The
polydienes, block copolymer, or branching agents
(hereinafter "polydienes"), are typically cationically
reactive and are present during the polymerization of the
butyl or halogenated butyl rubber, or can be blended with
the butyl rubber to form the SBB. The branching agent or
polydiene can be any suitable branching agent, and the
invention is not limited to the type of polydiene or
branching agent used to make the SBB.
[0029] In one embodiment, the SBB is a composition of
butyl or halogenated butyl rubber as described above and
a copolymer of a polydiene and a partially hydrogenated
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polydiene selected from the group consisting of styrene,
polybutadiene, polyisoprene, polypiperylene, natural
rubber, styrene-butadiene rubber, ethylene-propylene
diene rubber (EPDM), ethylene-propylene rubber (EPM),
styrene-butadiene-styrene and styrene-isoprene-styrene
block copolymers. Polydienes can be present, based on
the total monomer content in wt %, typically greater than
0.3 wt %; alternatively, about 0.3 to about 3 wt %; or
about 0. 4 to 2.7 wt 5.
[0030] Preferably the branched or "star-branched"
butyl rubber used herein is halogenated. In one
embodiment, the halogenated star-branched butyl rubber
("HSBB") comprises a butyl rubber, either halogenated or
not, and a polydiene or block copolymer, either
halogenated or not. The present invention is not limited
by the method of forming the HSBB. The polydiene/block
copolymer, or branching agents (hereinafter
"polydienes"), are typically cationically reactive and
are present during the polymerization of the butyl or
halogenated butyl rubber, or can be blended with the
butyl or halogenated butyl rubber to form the HSBB. The
branching agent or polydiene can be any suitable
branching agent, and the invention is not limited by the
type of polydiene used to make the HSBB.
[0031] A commercial embodiment of HSBB useful in the
present invention is Bromobutyl 6222 (ExxonMobil Chemical
Company), having a Mooney Viscosity (ML 1+8 at 125 C.,
ASTM D1646-04, modified) of about 27 to 37, and a bromine
content of about 2.2 to 2.6 wt %. Further, cure
characteristics of Bromobutyl 6222, as disclosed by the
manufacturer, are as follows: MH is from 24 to 38 dN m,
ML is from 6 to 16 dN m (ASTM D2084-92A).
[0032] Another elastomer useful in the invention is an
isoolefin-styrenic polymer. Useful isoolefin monomers
are C4 to C7 isoolefins such as isobutylene, 2-methyl-l-
butene, 3-methyl-l-butene, 2-methyl-2-butene, and 4-
methyl-l-pentene. Useful styrenic monomers in the
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isoolefin copolymer include styrene, alkylstyrene,
alkyloxystyrene, indene and indene derivatives, and
combinations thereof. The alkylstyrene may be an ortho-,
meta-, or para-alkyl-substituted styrene. In one
embodiment, the alkylstyrene is a p-alkylstyrene
containing at least 80%, more preferably at least 90% by
weight of the para-isomer. The polymer may also comprise
C4 to C14 multiolefin derived units such as isoprene,
butadiene, 2,3-dimethyl-1,3-butadiene, myrcene, 6,6-
dimethyl-fulvene, hexadiene, cyclopentadiene, and
piperylene. The polymer may also include functionalized
interpolymers wherein at least some of the alkyl
substituent groups present on the styrene monomer units
contain halogen or another functional group described
further below. These interpolymers are herein referred
to as "isoolefin copolymers comprising a
halomethylstyrene" or simply "isoolefin copolymer."
[0033] Such isoolefin polymers may be characterized as
interpolymers containing the following monomer units
randomly spaced along the polymer chain:
(1) (2)
H II
__________________________ C11-^-"-
410 14111
R C __ II
wherein R and Rl are independently hydrogen, lower alkyl,
preferably C1 to C7 alkyl and primary or secondary alkyl
halides and X is a functional group such as halogen.
Desirable halogens are chlorine, bromine or combinations
thereof, preferably bromine. Preferably R and Rl are each
hydrogen. The -CRR11-1 and -CRRiX groups can be substituted
on the styrene ring in either the ortho, meta, or para
positions, preferably the para position. Up to 60 mole %
of the p-substituted styrene present in the interpolymer
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structure may be the functionalized structure (2) above
in one embodiment, and in another embodiment from 0.1 to
mol %. In yet another embodiment, the amount of
functionalized structure (2) is from 0.4 to 1 mol %. The
5 functional group X may be halogen or some other
functional group which may be incorporated by
nucleophilic substitution of benzylic halogen with other
groups such as carboxylic acids; carboxy salts; carboxy
esters, amides and imides; hydroxy; alkoxide; phenoxide;
thiolate; thioether; xanthate; cyanide; cyanate; amino
and mixtures thereof. These functionalized isomonoolefin
copolymers, their method of preparation, methods of
functionalization, and cure are more particularly
disclosed in U.S. Pat. No. 5,162,445.
[0034] Useful in the invention are copolymers of
isobutylene and p-methylstyrene containing from 0. 5 to
mole % p-methylstyrene wherein up to 60 mole % of the
methyl substituent groups present on the benzyl ring
contain a bromine or chlorine atom, preferably a bromine
20 atom (p-bromomethylstyrene), as well as acid or ester
functionalized versions thereof wherein the halogen atom
has been displaced by maleic anhydride or by acrylic or
methacrylic acid functionality. These interpolymers are
termed "halogenated poly(isobutylene-co-p-methylstyrene)"
or "brominated poly(isobutylene-co-p-methylstyrene)". It
is understood that the use of the terms "halogenated" or
"brominated" are not limited to the method of
halogenation of the copolymer, but merely descriptive of
the copolymer which comprises the isobutylene derived
units, the p-methylstyrene derived units, and the p-
halomethylstyrene derived units.
[0035] These functionalized polymers preferably have a
substantially homogeneous compositional distribution such
that at least 95% by weight of the polymer has a p-
alkylstyrene content within 10% of the average p-
alkylstyrene content of the polymer. More preferred
polymers are also characterized by a narrow molecular
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weight distribution (Mw/Mn) of less than 5, more
preferably less than 2.5, a preferred viscosity average
molecular weight in the range of about 200,000 to about
2,000,000 and a preferred number average molecular weight
in the range of about 25,000 to about 750,000 as
determined by gel permeation chromatography.
[0036] Preferred halogenated poly(isobutylene-co-p-
methylstyrene) polymers are brominated polymers which
generally contain from about 0.1 to about 5 wt % of
bromomethyl groups. In yet another embodiment, the
amount of bromomethyl groups is about 0.2 to about 2.5 wt
%. Expressed another way, preferred copolymers contain
about 0.05 to about 2.5 mole % of bromine, based on the
weight of the polymer, more preferably about 0.1 to about
1.25 mole bromine, and are substantially free of ring
halogen or halogen in the polymer backbone chain. In one
embodiment of the invention, the interpolymer is a
copolymer of C4 to C/ isomonoolefin derived units, p-
methylstyrene derived units and p-halomethylstyrene
derived units, wherein the p-halomethylstyrene units are
present in the interpolymer from about 0.4 to about 1 mol
% based on the interpolymer. In another embodiment, the
p-halomethylstyrene is p-bromomethylstyrene. The Mooney
Viscosity (1+8, 125 C., ASTM D1646-04, modified) is about
30 to about 60 Mooney units.
[0037] The elastomer useful in the air permeation
prevention layer and the halogenated isobutylene
containing elastomer useful in the tie layer may be the
same or different elastomer. In a preferred embodiment,
the elastomer present in the air permeation prevention
layer and the halogenated isobutylene containing
elastomer present in the tie layer are the same
elastomer. In a preferred embodiment, the elastomer
present in the air permeation prevention layer and the
halogenated isobutylene containing elastomer present in
the tie layer are different elastomers. Preferably, the
elastomer present in the air permeation prevention layer
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is a brominated copolymer of isobutylene and para-methyl
styrene and the isobutylene containing elastomer present
in the tie layer is a brominated butyl rubber.
Thermoplastic Engineering Resin
[0038] For purposes of the present invention, the
thermoplastic engineering resin (also called an
"thermoplastic resin," or "thermoplastic") is defined to
be any thermoplastic polymer, copolymer or mixture
thereof having a Young's modulus of more than 500 MPa
and, preferably, an air permeation coefficient of less
than 60x10-12 cc cm/cm2 sec cm Hg (at 30 C), preferably
less than 25x10-12 cc cm/cm2 sec cm Hg (at 30 C),
including, but not limited to, one or more of the
following:
a) polyamide resins: nylon 6 (N6), nylon 66 (N66),
nylon 46 (N46), nylon 11 (N11), nylon 12 (N12), nylon 610
(N610), nylon 612 (N612), nylon 6/66 copolymer (N6/66),
nylon 6/66/610 (N6/66/610), nylon MXD6 (MXD6), nylon 6T
(N6T), nylon 6/6T copolymer, nylon 66/PP copolymer, nylon
66/PPS copolymer;
b) polyester resins: polybutylene terephthalate
(PBT), polyethylene terephthalate (PET), polyethylene
isophthalate (PEI), PET/PEI copolymer, polyacrylate
(PAR), polybutylene naphthalate (PEN), liquid crystal
polyester, polyoxalkylene diimide diacid/polybutyrate
terephthalate copolymer and other aromatic polyesters;
c) polynitrile resins: polyacrylonitrile (PAN),
polymethacrylonitrile, acrylonitrile-styrene copolymers
(AS), methacrylonitrile-styrene copolymers,
methacrylonitrile-styrene-butadiene copolymers;
d) polymethacrylate resins: polymethyl methacrylate,
polyethylacrylate;
e) polyvinyl resins: vinyl acetate (EVA), polyvinyl
alcohol (PVA), ethylene vinyl alcohol copolymers (EVOH),
polyvinylidene chloride (PVDC), polyvinyl chloride (PVC),
polyvinyl/polyvinylidene copolymer, polyvinylidene
chloride/methacrylate copolymer;
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f) cellulose resins: cellulose acetate, cellulose
acetate butyrate;
g) fluorine resins: polyvinylidene fluoride (PVDF),
polyvinyl fluoride (PVF), polychlorofluoroethylene
(PCTFE), tetrafluoroethylene/ethylene copolymer (ETFE);
h) polyimide resins: aromatic polyimides;
i) polysulfones;
j) polyacetals;
k) polyactones;
1) polyphenylene oxide and polyphenylene sulfide;
m) styrene-maleic anhydride;
n) aromatic polyketones; and
o) mixtures of any and all of a) through n)
inclusive as well as mixtures of any of the illustrative
or exemplified engineering resins within each of a)
through n) inclusive.
[0039] For purposes of the present invention, this
definition of engineering resin excludes polymers of
olefins having any degree of crystallinity, such as
polyethylene and polypropylene.
[0040] Preferred engineering resins include polyamide
resins and mixtures thereof; particularly preferred
resins include Nylon 6, Nylon 66, Nylon 6/66 copolymer,
Nylon 11, and Nylon 12 and their blends.
Additional components
[0041] Generally, elastomeric polymers, e.g., those
used to produce tires, are cross-linked or vulcanized.
Crosslinking or vulcanization is accomplished by
incorporation of curing agents and/or accelerators; the
overall mixture of such agents being typically referred
to as a cure "system. " It is known that the physical
properties, performance characteristics, and durability
of vulcanized rubber compounds are directly related to
the number (crosslink density) and types of crosslinks
formed during the vulcanization reaction. Curing agents
include those components described above that facilitate
or influence the cure of elastomers, and generally
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include metals, accelerators, sulfur, peroxides, and
other agents common in the art, and as described above.
Crosslinking or curing agents include at least one of,
e.g., sulfur, zinc oxide, and fatty acids and mixtures
thereof. Peroxide-containing cure systems may also be
used. Generally, polymer compositions may be cross-
linked by adding curative agents, for example sulfur,
metal oxides (i.e., zinc oxide, Zn0), organometallic
compounds, radical initiators, etc. and heating the
composition or mixture. When the method known as
"dynamic vulcanization" is used, the process is modified
so as to substantially simultaneously mix and vulcanize,
or crosslink, at least one of the vulcanizable components
in a composition comprising at least one vulcanizable
rubber, elastomer or polymer and at least one elastomer
or polymer not vulcanizable using the vulcanizing
agent(s) for the at least one vulcanizable component.
(See, e.g., U.S. Pat. No. 6,079,465 and the references
cited therein). In particular, the following are common
curatives that can function in the present invention:
ZnO, CaO, MgO, A1203, Cr03, FeO, Fe203, and NiO. These
metal oxides can be used in conjunction with the
corresponding metal stearate complex (e.g., the stearate
salts of Zn, Ca, Mg, and Al), or with stearic acid, and
either a sulfur compound or an alkyl peroxide compound.
To the curative agent(s) there are often added
accelerators for the vulcanization of elastomer
compositions. The curing agent(s), with or without the
use of at least one accelerator, is often referred to in
the art as a curing "system" for the elastomer(s). A
cure system is used because typically more than one
curing agent is employed for beneficial effects,
particularly where a mixture of high diene rubber and a
less reactive elastomer is used.
[0042] For purposes of dynamic vulcanization in the
presence of an engineering resin to form the highly
impermeable layer, any conventional curative system which
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is capable of vulcanizing saturated halogenated polymers
may be used to vulcanize at least the elastomeric
halogenated copolymer of a C4 to C7 isomonoolefin and a
para-alkylstyrene, except that peroxide curatives are
specifically excluded from the practice of this invention
when the thermoplastic engineering resin(s) chosen are
such that peroxide would cause these resins themselves to
crosslink since the engineering resin would itself
vulcanize or crosslink, thereby resulting in an
excessively cured, non-thermoplastic composition.
Suitable curative systems for the elastomeric halogenated
copolymer component of the present invention include zinc
oxide in combination with zinc stearate or stearic acid
and, optionally, one or more of the following
accelerators or vulcanizing agents: Permalux, the di-
ortho-tolylguanidine salt of dicatechol borate; HVA-2 (m-
phenylene bis maleimide); Zisnet, 2,4,6-trimercapto-5-
triazine; ZDEDC (zinc diethyl dithiocarbamate) and also
including for the purposes of the present invention,
other dithiocarbamates; Tetrone A (dipentamethylene
thiuram hexasulfide); Vultac 5 (alkylated phenol
disulfide), 5P1045-(phenol formaldehyde resin); 5P1056
(brominated alkyl phenol formaldehyde resin); DPPD
(diphenyl phenylene diamine); salicylic acid, ortho-
hydroxy benzoic acid; wood rosin, abietic acid; and TMTDS
(tetramethyl thiuram disulfide), used in combination with
sulfur.
[0043] Dynamic vulcanization is conducted at
conditions to vulcanize at least partially, preferably
fully, the elastomeric halogen containing copolymer of
the fluid (gas or liquid, preferably air) permeation
prevention layer.
[0044] With reference to the polymers and/or
elastomers referred to herein, the terms "cured,"
"vulcanized," or "cross-linked" refer to the chemical
reaction comprising forming bonds as, for example, during
chain extension, or crosslinks between polymer chains
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comprising the polymer or elastomer to the extent that
the elastomer undergoing such a process can provide the
necessary functional properties resulting from the curing
reaction when the tire is put to use. For purposes of
the present invention, absolute completion of such curing
reactions is not required for the elastomer-containing
composition to be considered "cured," "vulcanized" or
"cross-linked." For example, for purposes of the present
invention, a tire comprising the tie layer is
sufficiently cured when the tire of which it is a
component passes the necessary product specification
tests during and after manufacturing and performs
satisfactorily when used on a vehicle. Furthermore, the
composition is satisfactorily, sufficiently or
substantially cured, vulcanized or cross-linked when the
tire can be put to use even if additional curing time
could produce additional crosslinks. With limited
experimentation using known tools and standard
techniques, one of ordinary skill in the art can readily
determine the appropriate or optimum cure time required
for the elastomer(s) and polymer(s) selected for use in
the tie layer composition, as well as the amount and type
of crosslinking agent(s) and accelerator(s) and the
curing temperature that will be used to manufacture the
tire.
[0045] Accelerators useful herein include amines,
guanidines, thioureas, thiazoles, thiurams, sulfenamides,
sulfenimides, thiocarbamates, xanthates, and the like.
Acceleration of the cure process may be accomplished by
adding to the composition an amount of the accelerant.
The mechanism for accelerated vulcanization of natural
rubber involves complex interactions between the
curative, accelerator, activators and polymers. Ideally,
all of the available curative is consumed in the
formation of effective crosslinks which join together two
polymer chains and enhance the overall strength of the
polymer matrix. Numerous accelerators are known in the
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art and include, but are not limited to, the following:
stearic acid, diphenyl guanidine (DPG),
tetramethylthiuram disulfide (TMTD), 4,4'-
dithiodimorpholine (DTDM), tetrabutylthiuram disulfide
(TBTD), 2,2'-benzothiazyl disulfide (MBTS),
hexamethylene-1,6-bisthiosulfate disodium salt dihydrate,
2-(morpholinothio) benzothiazole (MBS or MOR),
compositions of 90% MOR and 10% MBTS (MOR90), N-
tertiarybutyl-2-benzothiazole sulfenamide (TIBBS), and N-
oxydiethylene thiocarbamyl-N-oxydiethylene sulfonamide
(OTOS), zinc 2-ethyl hexanoate (ZEH), N,N'-diethyl
thiourea. Curatives, accelerators and cure systems
useful with one or more crosslinkable polymers are well-
known in the art.
[0046] In one embodiment of the invention, at least
one curing agent is typically present at about 0.1 to
about 15 phr; alternatively at about 0.5 to about 10 phr.
[0047] The composition described herein may have one
or more filler components such as calcium carbonate,
clay, mica, silica and silicates, talc, titanium dioxide,
starch and other organic fillers such as wood flour, and
carbon black. Suitable filler materials include carbon
black such as channel black, furnace black, thermal
black, acetylene black, lamp black and the like.
Reinforcing grade carbon black is most preferred. The
filler may also include other reinforcing or non-
reinforcing materials such as silica, clay, calcium
carbonate, talc, titanium dioxide and the like. The
filler is normally present in the composition (preferably
the innerliner) at a level of from about 20 to about 50%
by weight of the total composition, more preferably from
about 25 to 40% by weight. In one embodiment, the filler
is carbon black or modified carbon black. A preferred
filler is semi-reinforcing grade carbon black, typically
used at a level of about 10 to 150 parts per hundred of
rubber, by weight (phr), more preferably about 30 to
about 120 phr. Grades of carbon black useful herein
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include N110 to N990, as described in RUBBER TECHNOLOGY
59-85 (1995). More desirably, grades of carbon black
useful in, for example, tire treads, such as N229, N351,
N339, N220, N234 and N110 provided in ASTM (D3037, D1510,
and D3765) are useful herein. Embodiments of carbon
black useful in, for example, tire sidewalls such as
N330, N351, N550, N650, N660, and N762 are particularly
useful herein. Embodiments of carbon black useful in,
for example, innerliners or inner tubes, such as N550,
N650, N660, N762, N990, and Regal 85 (Cabot Corporation,
Alpharetta, Ga. ) and the like are similarly particularly
useful herein.
[0048] Compatibilizers may be employed due to the
difference in solubility of the thermoplastic resins and
elastomers in the DVA. Such compatibilizers are thought
to function by modifying, and in particular reducing, the
surface tension between the rubber and thermoplastic
components of the composition. Suitable compatibilizers
include ethylenically unsaturated nitrile-conjugated
diene-based high saturation copolymer rubbers (HNBR),
epoxylated natural rubbers (ENR), acrylate rubber, and
mixtures thereof, as well as copolymers having the same
structure of the thermoplastic resin or the elastomeric
polymer, or a structure of a copolymer having an epoxy
group, carbonyl group, halogen group, amine group,
maleated group, oxazoline group, or hydroxyl group
capable of reacting with the thermoplastic resin or the
elastomer.
[0049] The amount of compatibilizer is typically about
0.5 to about 10 parts by weight; preferably about 3 to
about 8 parts by weight, based upon 100 parts by weight
of the total of the elastomer.
[0050] Minimizing the viscosity differential between
the elastomer and the thermoplastic resin components
during mixing and/or processing enhances uniform mixing
and fine blend morphology that significantly enhance good
blend mechanical as well as desired permeability
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properties. However, as a consequence of the flow
activation and shear thinning characteristic inherent in
elastomeric polymers, reduced viscosity values of the
elastomeric polymers at the elevated temperatures and
shear rates encountered during mixing are much more
pronounced than the reductions in viscosity of the
thermoplastic component with which the elastomer is
blended. It is desired to reduce this viscosity
difference between the materials to achieve a DVA with
acceptable elastomeric dispersion sizes.
[0051] Components previously used to compatibilize the
viscosity between the elastomer and thermoplastic
components include low molecular weight polyamides,
maleic anhydride grafted polymers having a molecular
weight on the order of 10,000 or greater, methacrylate
copolymers, tertiary amines and secondary diamines.
Examples include maleic anhydride-grafted ethylene-ethyl
acrylate copolymers (a solid rubbery material available
from Mitsui-DuPont as AR-201 having a melt flow rate of 7
g/10 min measured per JIS K6710) and
butylbenzylsulfonamide (BBSA). These compounds may act
to increase the 'effective' amount of thermoplastic
material in the elastomeric/thermoplastic compound. The
amount of additive is selected to achieve the desired
viscosity comparison without negatively affecting the
characteristics of the DVA. If too much is present,
impermeability may be decreased and the excess may have
to be removed during post-processing. If not enough
compatibilizer is present, the elastomer may not invert
phases to become the dispersed phase in the thermoplastic
resin matrix.
[0052] The amount of plasticizer present in the DVA
ranges in amounts from a minimum amount of about 2 phr, 5
phr, or 10 phr to a maximum amount of 15 phr, 20 phr, 25
phr, 30 phr, or 35 phr.
Preparation of the DVA
[0053] The term "dynamic vulcanization" is used herein
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to denote a vulcanization process in which the
engineering resin and the rubber are mixed under
conditions of high shear and elevated temperature in the
presence of a curing agent. As a result, the rubber is
simultaneously cross-linked and dispersed as fine
particles, for example, in the form of a microgel, within
the engineering resin which forms a continuous matrix;
the resulting composition is known in the art as a
"dynamically vulcanized alloy" or DVA. Dynamic
vulcanization is effected by mixing the ingredients at a
temperature which is at or above the curing temperature
of the rubber using in the equipment such as roll mills,
Banbury mixers, continuous mixers, kneaders, or mixing
extruders (such as twin screw extruders). The unique
characteristic of the dynamically cured composition is
that, notwithstanding the fact that the rubber is cured,
the composition can be processed and reprocessed by
conventional thermoplastic processing techniques such as
extrusion, injection molding, compression molding, etc.
Scrap and or flashing can also be salvaged and
reprocessed.
[0054] The dynamic
vulcanization process is conducted
at conditions to vulcanize at least partially, preferably
fully, the elastomeric halogen-containing copolymer. To
accomplish this, the thermoplastic engineering resin, the
elastomeric copolymer and optional other polymers, are
mixed together at a temperature sufficient to soften the
resin or, more commonly, at a temperature above the
melting point of a crystalline or semi-crystalline resin.
Preferably the cure system is premixed in the elastomer
component. Heating and masticating at vulcanization
temperatures are generally adequate to complete
vulcanization in about 0. 5 to about 10 minutes. The
vulcanization time can be reduced by elevating the
temperature of vulcanization. A suitable range of
vulcanization temperatures is typically from about the
melting point of the thermoplastic resin to about 300 C;
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for example, the temperature may range from about the
melting point of the matrix resin to about 275 C.
Preferably, the vulcanization is carried out at a
temperature range from about 10 C to about 50 C above
the melting temperature of the matrix resin.
[0055] It is preferred that the mixing process be
continued until the desired level of vulcanization or
crosslinking is completed. If vulcanization is permitted
to continue after mixing has stopped, the composition may
not be reprocessable as a thermoplastic. However,
dynamic vulcanization can be carried out in stages. For
example, vulcanization can be commenced in a twin screw
extruder and pellets formed of the DVA material or
material using an underwater pelletizer, thereby
quenching the vulcanization before it is completed. The
vulcanization process can be completed at a later time
under dynamic vulcanization conditions. Those of
ordinary skill in the art will appreciate the appropriate
quantities, types of curatives and extent of mixing time
required to carry out the vulcanization of the rubber.
Where necessary or desirable to establish the appropriate
concentrations and conditions, the rubber alone can be
vulcanized using varying amounts of curative, which may
include one or more curatives and/or accelerators, to
determine the optimum cure system to be utilized and the
appropriate cure conditions to achieve a substantially
full cure.
[0056] While it is preferred that all components be
present in the mixture prior to carrying out the dynamic
vulcanization process, this is not a necessary condition.
For example, it is not necessary to add all of the
fillers and oil, when used, prior to the dynamic
vulcanization stage. A portion or all of the fillers and
oil can be added after the vulcanization is completed.
Certain ingredients, such as stabilizers and process aids
function more effectively if they are added after curing.
Adhesive Tie Layer
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[0057] The tie layer is typically present as a sheet
or film that is formed by the use of extrusion or
calendering processes. The tie layer may co-extruded
with the DVA or extruded or calendered onto an already
formed DVA layer.
[0058] The adhesive tie layer composition comprises a
mixture of: (1) 100 weight % of a halogenated
isobutylene-containing elastomer; (2) about 20 to about
50 weight % of at least one filler; (3) about 0 to about
30 weight % of at least one processing oil; (4) at least
about 0. 1 to about 15 parts per hundred of rubber (phr)
of a curing system for the elastomers; and (5) .1 to
about 10 parts per hundred of at least one tackifier. In
a preferred embodiment the halogenated isobutylene-
containing elastomer is a halogen-containing random
copolymer of isobutylene and a C4 to C14 multiolefin. In
each instance, the halogen is selected from the group
consisting of chlorine, bromine and mixtures thereof.
Useful elastomers may be selected from the group
consisting of chlorinated butyl rubber, brominated butyl
rubber, chlorinated star branched butyl rubber,
brominated star branched butyl rubber, and mixtures
thereof. The selection of 100 wt% of the halogenated
isobutylene-containing elastomer as the sole elastomer in
the tie layer provides for low permeability in the tie
layer.
[0059] Fillers useful in the tie layer include at
least one filler is selected from the group consisting of
carbon black, clay, exfoliated clay, intercalated clay,
dispersed clay, calcium carbonate, mica, silica,
silicates, talc, titanium dioxide, wood flour and
mixtures thereof. Preferably, the filler is selected
from the group consisting of carbon black, exfoliated
clay, intercalated clay, and dispersed clay, and mixtures
thereof. The amount of the at least one filler is
typically about 20 to about 50 weight %; preferably about
25 to about 40 weight %; based on the total weight of the
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tie layer composition.
[0060] The tie layer optionally includes a rubber
process or plasticizer oil. As used herein, the term
"process oil" means both the petroleum derived process
oils and synthetic plasticizers. Such oils are primarily
used to Improve the processing of the composition during
preparation of the layer, e.g., mixing, calendering, etc.
Generally, the process oil may be selected from
paraffinic oils, aromatic oils, naphthenic oils, and
polybutene oils. Polybutene process oil is a low
molecular weight (less than 15,000 Mn) homopolymer or
copolymer of olefin-derived units having from about 3 to
about 8 carbon atoms, more preferably about 4 to about 6
carbon atoms. In another embodiment, the polybutene oil
is a homopolymer or copolymer of a C4 raffinate.
Preferred polybutene processing oils are typically
synthetic liquid polybutenes having a certain molecular
weight, preferably from about 420 Mn to about 2700 Mn.
The molecular weight distribution-Mw/Mn-("MWD") of
preferred polybutene oils is typically about from 1.8 to
about 3, preferably about 2 to about 2.8. The preferred
density (g/ml) of useful polybutene processing oils
varies from about 0.85 to about 0.91. The bromine number
(CG/G) for preferred polybutene oils ranges from about 40
for the 450 Mn process oil, to about 8 for the 2700 Mn
process oil.
[0061] Rubber process oils also have ASTM designations
depending on whether they fall into the class of
paraffinic, naphthenic or aromatic hydrocarbonaceous
process oils. The type of process oil utilized will be
that customarily used in conjunction with a type of
elastomer component and a rubber chemist of ordinary
skill in the art will recognize which type of oil should
be utilized with a particular rubber in a particular
application.
[0062] Suitable plasticizer oils include aliphatic
acid esters or hydrocarbon plasticizer oils such as
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paraffinic or naphthenic petroleum oils or polybutene
oils.
[0063] In still another embodiment, naphthenic,
aliphatic, paraffinic and other aromatic oils are
substantially absent from the composition. By
"substantially absent", it is meant that naphthenic,
aliphatic, paraffinic and other aromatic oils may be
present, if at all, to an extent no greater than 1 phr in
the composition. In still another embodiment,
naphthenic, aliphatic, paraffinic and other aromatic oils
are present at less than 2 phr.
[0064] The amount of the rubber process oil or
plasticizer oil is typically about 0 to about 30 weight
%; preferably about 0 to about 20 weight %; more
preferably about 0 to about 10 weight %, based on the
total weight of the tie layer composition. Preferably,
the process oil is a naphthenic or polybutene type oil.
[0065] The adhesive tie layer is cured or vulcanized
using a cure system comprising at least one curing agent
and at least one accelerator useful for the halogenated
isobutylene-containing elastomers comprising the
composition. The cure system for the adhesive tie layer
includes all the above identified curing agents and
accelerators already described above as useful in the
DVA. The cure systems in the DVA and the tie layer may
or may not be identical; but should be compatible due to
interlayer transfer of the cure system components from
one layer to the adjacent layer when the layers are
adjacent to each other during formation and subsequent
article construction and article curing. Typically, the
cure system is present in the amount of at least about 0.
1 to about 15 parts per hundred of rubber (phr),
although, as one of ordinary skill in the art will know,
the specific amount of the cure system is not limited and
the amount used will depend, in large measure, on the
particular components of the cure system selected.
[0066] Further optional, useful additives are
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typically added at a level of less than about 10 phr and
can be selected from the group consisting of pigments,
antioxidants, antiozonants, processing aids, compound
compatibilizers, and the like and mixtures thereof. Such
optional additives can be included at the discretion of
the compounder in order to achieve a particular advantage
in the composition, e.g., the use of a tackifier to
improve contact adhesion during tire building or an
antioxidant to improve heat aging characteristics of the
cured composition.
[0067] In a preferred embodiment at least one
tackifier is included in the tie layer composition. For
purposes of the present invention, a tackifier includes
materials identified as rosins or rosin derivatives as
well as various derivatives such as acetylene-phenolic
compounds that are known as tackifiers for elastomer or
polymer containing compositions. Particularly useful
tackifiers include condensation products of butyl phenol
and acetylene, such as acetylene-p-tert-butyl phenol,
available commercially as "Koresin" (BASF) and rosin
tackifier available commercially as "MR1085A" (Mobile
Rosin Oil Company, Mobile, Ala.), a blend of tall oil
rosin and fatty acids. Some tackifiers are designated as
particularly useful for imparting tack to specific
polymers or elastomers, but it may be determined that
they are also useful for compounds of the present
invention.
[0068] Tackiness generally refers to the ability of an
uncured rubber compound to stick to itself or to another
compound when the compounds are contacted using a
relatively short dwell time and only a moderate amount of
pressure ("Rubber Technology: Compounding and Testing for
Performance," J. S. Dick, Ed., 42, 2001). The dwell time
and pressure are often determined by the equipment used
for that purpose and by the potential for a sheet of the
uncured composition to be damaged by excessive pressure
and dwell time. Tack can also be affected by the
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solubility of the various rubber components in one
another as well as in the overall composition. In some
instances, a component of the composition may diffuse to
the surface of a calendered or extruded sheet or film and
either interfere with tack, for example, if it is an
inorganic particulate (sometime referred to as "bloom").
On the other hand such diffusion may improve tack, for
example, if the diffusing component is a one that itself
exhibits tack. It is appreciated by those skilled in the
art that tack is a difficult property to measure and, at
times one skilled in the art may be required to determine
if a composition has achieved a sufficient level of tack
by evaluating performance of the composition(s) in a
factory trial or environment in which the end product is
produced. In the present case, that will typically
involve actual tire building and a determination of
whether the tie layer exhibits sufficient tire building
tack so that the uncured tire construction will hold
together during the tire building stage and during
initial stages inflation during vulcanization until the
structure achieves a sufficient level of cure and,
consequently, cured adhesion of the various tire layers
to one another; including adhesion of the tie layer to
those layers that with which it is in proximate contact,
including, for example, the carcass layer and the
innerliner layer. There are no standardized test
procedures for measuring tack of rubber compounds, but a
widely used instrument is the "Tel-Tak Tackmeter,"
introduced by Monsanto in 1969. Another test instrument
is the PICMA tack tester made by Toyo Seiki Seisakusho
(Japan).
[0069] In a preferred embodiment of the present
invention, at least one tackifier is added to the tie
layer composition at a concentration of about 1 phr to
about 20 phr; preferably about 2 phr to about 18 phr;
more preferably about 3 phr to about 16 phr; for example,
about 4 phr to about 14 phr. Alternatively, the at least
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one tackifier is typically used at a level of about 15
phr or less; preferably about 12 phr or less; more
preferably about 10 phr or less; still more preferably
about 9 phr or less; most preferably about 8 phr or less;
such as, for example, about 1 phr to about 10 phr; about
1 phr to about 9 phr; about 2 phr to about 9 phr; about 2
phr to about 8 phr; about 2 phr to about 7 phr and the
like, including individual values and ranges including
each of the values, in phr, of about 1, 2, 3, 4, 5, 6, 7,
8, 9, and 10. Similarly, where a mixture of tackifiers
is used, such as for example two tackifiers of the same
or different chemical type, each of the tackifiers can be
present in equal amounts or in amounts that are not
equal, the total amount of tackifier used preferably
constrained by the total amounts recited immediately
above.
[0070] The adhesive tie layer composition can be
prepared using mixing equipment such as Banbury mixers,
mill roll mixers, extruder mixers and the like,
individually and in combination in order to mix the
elastomers, filler(s), processing oil and other additives
as well as to disperse the cure system components.
Typically, the ingredients other than the cure system
components are mixed at elevated temperature and high
shear to obtain satisfactory dispersion of all non-
elastomeric components into the elastomers and of the
elastomers in one another. After such a mixing step, the
composition absent the cure system components, sometimes
referred to as a masterbatch, is cooled to a lower
temperature using, e.g., a rubber mill or a lower
temperature, lower shear section of a mixing extruder or
an internal mixer and the cure system components are
dispersed into the masterbatch. The temperature for
mixing curatives is typically less than about 120 C,
preferably less than about 100 C.
[0071] The adhesive tie layer composition can be
formed into a layer suitable for the end use application,
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using, for example, an extruder or a calender. Where
convenient or useful, extrusion can include the use of
equipment allowing for the dual or multiple extrusion of
the fluid (preferably air) permeation prevention layer
and the adhesive tie layer. Alternatively, the adhesive
tie layer may be prepared by calendering the compounded
rubber composition into sheet material having the desired
thickness and cutting the sheet material into strips of
appropriate width and length for innerliner application
in a particular size or type tire.
[0072] In the invention, the tie layer is prepared for
use in a tire construction and has a thickness that is
typically about 5 mm or less; preferably about 2.5 mm or
less; more preferably about 1.0 mm or less, about 0.9 mm
or less, or about 0.8 mm or less; even more preferably
about 0.2 to about 2.0 mm; most preferably about 0.2 to
about 1.5 mm or about 0.2 mm to about 0.8 mm; for example
about 0.3 to about 0.9 mm. The thickness of the tie
layer for use in a hose construction can be the same or
different depending on the application in which the hose
will be employed. For example, an unreinforced, low
pressure hose can have different performance requirements
than a high pressure, reinforced hose and, similarly, a
hose intended for use with a liquid can differ from one
for use with a gas. Adjustment of the thickness is
within the skill of the product designer, engineer or
chemist, based, if necessary, on limited experimentation.
Layered Composition / Laminate Structure
[0073] After the DVA has been mixed to achieve the
desired composition and morphology, it is typical to pass
the material thru a pelletizer to form DVA pellets.
These pellets are then supplied to a film extruder to
prepare an extruded/blown film or a mixer to prepare a
cast film. In accordance with the present invention, the
DVA is extruder or cast by itself; i.e., the sheet is not
co-extruded with an adhesive film layer to create
addition adhesion between the DVA and the adhesive tie
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layer.
[0074] After the DVA film is formed, the film is
treated to remove any residual plasticizer or oils; in
the present invention, "residual plasticizer or oils" are
defined as plasticizer or oils that have not been grafted
into the DVA during mixing in the extruder or during
preparation of the film and which, due to the thinness of
the film, are present on the film surfaces. The removal
of the residual plasticizer/oils is done to obtain a film
that is substantially free of any plasticizer/oils
present on the film surface wherein 'substantially free'
is defined as less than 0.1 wt% of plasticizer on the
film.
[0075] One method of removing plasticizer/oils from
the DVA film is by exposure to heat to flash, evaporate,
sublime, and/or oxidize the plasticizer from at least one
surface of the film. This can be accomplished by heating
the film for a residence time at a temperature no higher
than 15 or 10 or 5 or 1 C above the flash point of the
plasticizer/oil and then cooling the DVA film to form a
heat-treated film having a level of plasticizer less than
the level of plasticizer in the originally prepared DVA
film. Desirably, the film is exposed to oxygen during
the heating step. In any embodiment of the invention, a
continuous or substantially continuous current of gas is
blown over the continuous elastomeric length while being
heated. The gas may be air, nitrogen/oxygen mixture, or
other gas with an oxidizer mixed therein.
[0076] Figure 1 shows a method of treating the DVA
film to remove the residual plasticizer. The DVA film 10
is passed through a multi-zone oven 12. The DVA film 10
is unwound off of rolls 14 and rewound onto rolls 16.
The multi-zone oven 12 is illustrated with four zones;
however, the number of actual zones useful in the
invention may vary from 2 to 10 zones. By employing
zones in the oven 12, the temperature of the DVA material
may be gradually raised or lowered to achieve either
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immediate or delayed removal of the residual
plasticizer/oils, as well as provide any desired gradual
cooling of the DVA film. In any embodiment of the
invention, flashing of the plasticizer/oils occurs in
zone N-2 wherein N is the total number of zones in the
oven 12 and the zones are counted in order from entry to
exit of the film 10.
[0077] The rewind roll 16 is illustrated as being
immediately adjacent to the exit of the oven 12; however,
it will be appreciated by those in the art that if the
treated reduced plasticizer film 18 has not reached a
sufficiently cooled down temperature to permit rewinding
of the film 10, additional take up and wrap rolls, as
well as other conventional cool-down means, may be
employed.
[0078] Alternatively, instead of the reduced
plasticizer film 18 being rewound onto rolls 16, the film
18 may be sent to calendering operation for application
of the adhesive tie gum layer. An exemplary calendering
system for application of the adhesive tie gum layer is
illustrated in Figure 2; as calendering applications are
well known, one skilled in the art would appreciate that
a variety of calendering systems may be useful in the
present invention and the invention is not limited by the
illustrated system. The DVA film 18 is passed around a
bank 20 of calender rolls. As the DVA film 18 passes
through several of the nips created by adjacent rolls, it
passed under a set of pencil banks 22 containing the
adhesive tie layer composition. The rolls are adjacent
to obtain the desired thickness to the adhesive tie
layer.
[0079] The rolls in calender bank 20 are heated to
warm up the DVA film 18 and to ensure that the adhesive
tie layer composition in the pencil banks 22 is of a
sufficient temperature to permit the elastomeric
composition to flow and smoothly coat the DVA film. The
temperature and pressure of the rolls in the bank 20
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should be sufficient to cause a degree of bonding between
the DVA film 18 and the adhesive tie composition. The
temperature of the rolls may vary from 50 C to 150 C,
preferably from 65 C to 85 C. The temperature should
remain below the vulcanization temperature of the tie
layer composition to prevent any curing of the adhesive
tie layer composition.
[0080] The film exits the calender bank 20 as a tie
layer coated film 24 (this may also be referred to as a
DVA laminate). For ease of windup, due to the tacky
nature of the adhesive tie composition, an optional
handling film 26 may be applied to the coated film 24 to
prevent the DVA laminate 24 from adhering to itself
during subsequent roll windup and storage. Prior to use
of the DVA laminate 24, if present, the handling film is
removed from the DVA laminate 24.
[0081] The compositions of the present invention and
layered structures formed using such compositions can be
used in tire applications; tire curing bladders; air
sleeves, such as air shock absorbers, diaphragms; and
hose applications, including gas and fluid transporting
hoses.
[0082] Figure 3 is a semi-cross-sectional view along
the meridian direction of a tire 28 illustrating a
typical example of the arrangement of an air permeation
prevention or innerliner layer of a pneumatic tire. At
least one carcass layer 30 spans between the left and
right bead cores 32 (note that, since only one-half of
the symmetrical cross-section view is included for
simplicity, the second bead core is not illustrated). On
the tire inner surface, inside of the carcass layer 30
there is provided an innerliner layer 34. Interposed
between the innerliner layer 34 and the carcass layer 30
is the adhesive tie layer 36. The adhesive tie layer 36
facilitates the adhesion and air holding qualities of the
DVA air permeation prevention layer to the inner surface
of the tire. The surface of the tie layer 36 opposite
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the surface that is in contact with the innerliner layer
34 is in direct contact with the innermost carcass layer
30, or more particularly, the adhesive tie layer 36 is in
direct contact with the radially innermost coating
compound of the innermost carcass layer 30.
[0083] The pneumatic tire is also comprised of an
outer surface which includes the tread, belt structure
composed of multiple layers, and sidewall elements, and
possible intermediate carcass layer which comprises a
number of plies containing tire reinforcing fibers,
(e.g., rayon, polyester, nylon or metal fibers) embedded
in a rubbery matrix. Variations it the tread, belt, and
carcass layers, as well as the size of the tire (i.e.,
overall diameter and sidewall height) are permissible and
are not limited by the present invention. Tires are
normally built on a tire forming drum using the layers
described above. After the uncured tire has been built
on the drum, it is removed and placed in a heated mold.
The mold contains an inflatable tire shaping bladder that
is situated within the inner circumference of the uncured
tire. After the mold is closed the bladder is inflated
and it shapes the tire by forcing it against the inner
surfaces of the closed mold during the early stages of
the curing process. The heat within the bladder and mold
raises the temperature of the tire to vulcanization
temperatures. Vulcanization temperatures are typically
about 100 C to about 250 C; preferably about 150 C to
about 200 C. Cure time may vary from about one minute to
several hours; preferably from about 5 to 30 minutes.
Cure time and temperature depend on many variables well
known in the art, including the composition of the tire
components, including the cure systems in each of the
layers, the overall tire size and thickness, etc.
Vulcanization parameters can be established with the
assistance of various well-known laboratory test methods,
including the test procedure described in ASTM D2084-01,
(Standard Test Method for Rubber Property-Vulcanization
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Using Oscillating Disk Cure Meter) as well as stress-
strain testing, adhesion testing, flex testing, etc.
Vulcanization of the assembled tire results in complete
or substantially complete vulcanization or crosslinking
of all elements or layers of the tire assembly, i.e., the
innerliner, the carcass and the outer tread and sidewall
layers. In addition to developing the desired strength
characteristics of each layer and the overall structure,
vulcanization enhances adhesion between these elements,
resulting in a cured, unitary tire from what were
separate, multiple layers.
[0084] As discussed in detail above, the innerliner
layer exhibits advantageously low permeability properties
and preferably comprises a dynamically vulcanized
composition comprising an engineering resin, particularly
polyamide, and a halogenated isobutylene-para-
methylstyrene copolymer. Furthermore, as a consequence
of the unique composition of the tie layer based on a
vulcanizable halogenated isobutylene elastomer, in
particular its low air permeability property and ability
to generate high vulcanized adhesion to the innerliner
layer surface in which it is in contact, allows for the
use of a thin tie layer compared to compositions
containing primarily high diene rubber. The resulting
overall structure based on such innerliner and tie layers
allows for a tire construction (as well as other
constructions comprising an air or fluid holding layer
and tie layer) having reduced weight. Typically about 2%
to about 16% weight savings can be realized;
alternatively, about 4% to about 13% weight savings.
Such improvements are particularly meaningful in an
application such as pneumatic tires.
[0085] The following examples are provided as specific
illustrations of embodiments of the claimed invention.
It should be understood, however, that the invention is
not limited to the specific details set forth in the
examples. Furthermore, any range of numbers recited in
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the specification or claims, such as that representing a
particular set of properties, units of measure,
conditions, physical states or percentages, is intended
to literally incorporate expressly herein by reference or
otherwise, any number falling within such range,
including any subset of numbers within any range so
recited. For example, whenever a numerical range with a
lower limit, RL, and an upper limit Ru, is disclosed, any
number R falling within the range is specifically
disclosed. In particular, the following numbers R within
the range are specifically disclosed: R=RL+k(R,-RL), where
k is a variable ranging from 1% to 100% with a 1%
increment, e.g., k is 1%, 2%, 3%, 4%, 5% . . . 50%, 51%,
52% . . . . 95%, 96%, 97%, 98%, 99%, or 100%. Moreover,
any numerical range represented by any two values of R,
as calculated above is also specifically disclosed.
EXAMPLES
[0086] Compositions and samples were prepared
according to the following examples. The amount of each
component used is based on parts per hundred rubber (phr)
present in the composition. The following commercially
available products were used for the components employed
in the compositions of the examples:
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Table 1
Components Description
Elastomers
BIIR Bromobutyl Tm 2222 (brominated isobutylene-
isoprene copolymer, 2-,)5 Br, ExxonMobil Chemical
Company, Houston Texas)
BIMS Brominated isobutylene p-methylstyrene
copolymer, 1.2 molt Br, 7.5 wt% PMS
BIMS-2 Brominated isobutylene p-methylstyrene
copolymer, 0.75 molt Br, 5 wt% PMS
NR Natural Rubber: SMR-20, Standard Malaysian
Rubber
SBR Styrene-butadiene rubber, 23.51 bound styrene:
Capo 1502, DSM
Cure System Components
ZnO Zinc oxide
St-acid Stearic acid
ZnSt Zinc stearate
Sulfur
MBTS 2,2'-benzothiazyldisulfide; sulfur-containing
cure accelerator
Elastomeric Additive components
Struktol 40M5 Compatibilizer: mixture of dark aromatic
hydrocarbon resins, Struktol Company
Process Oil naphthenic processing oil: Calsol 810, Calumet
Lubricants
Flectol Flectol TMQ antioxidant: polymerized 1,2-
dihydro-2,2,4-trimethylguinoline, Flexsys
America
N660 semi-reinforcing grade carbon black
N351 semi-reinforcing grade carbon black
Ti alkyl phenolformaldehyde resin: SP1068
Schenectady International
T2 brominated octylphenol resin: SP1055
Schenectady International
T3 Compound of rosin acid: MR1085A, Mobil Rosin
Oil Company
T4 Acetylene-p-tert-butyl phenol condensation
product: Koresin, BASF
Engineering Resin Component
N6/66 Nylon 6/66 copolymer available as Ube 5033B
from Ube
Engineering Resin Additive Components
Plasticizer N-butylbenzenesulfonamide, BM-4, Daihachi
Chemical Ind.
Compatibilizer maleated ethylene vinylacetate (EVA) copolymer,
AR201, DuPont-Mitsui
Stabilizer package includes Irganox, Tinuvin, and Copper
Iodide(CuI)
[0087] The testing methods used to evaluate the
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following samples are set forth in Table 2.
TABLE 2
Tensile Strength (UTS) ISO-37 ASTM D412 Samples press cured, 5 minutes
(MPa) 207 C, 2mm thickness
Elongation at break (%) ISO-37 ASTM D412
300 Modulus (MPa) ISO-37 ASTM D4l2
Hardness Shore A ASTM D2240
Tear Strength N/m ASTM D624
Peel Adhesion Force required to separate the two layers at
23 C
[0088] A DVA of thermoplastic elastomeric having the
composition as set forth in Table 3 was prepared. The
elastomer component and vulcanization system were charged
into a first kneader, mixed for approximately 3.5
minutes, and dumped out at about 90 C to prepare an
accelerated elastomer component with a vulcanization
system. The mixture was then pelletized by a rubber
pelletizer. Next, the pelletized elastomer and resin
components were charged into a twin screw mixing extruder
and dynamically vulcanized to prepare a thermoplastic
elastomer composition. The DVA was prepared according to
the procedure described in EP 0 969 039, with specific
reference to the section entitled "Production of
Thermoplastic Elastomer Composition." The vulcanization
in the twin-screw extruder was done at 230 C. After the
DVA was prepared and pelletized, it was then sent to a
film blowing operation wherein the DVA was extruded as a
extruded thin film. In accordance with the present
invention, the DVA film was not co-extruded with an
adhesive coating; the DVA film was adhesive free.
TABLE 3
Component Amount, phr
BIMS 100
ZnO 0.15
St-acid 0.60
ZnSt 0.30
N6/66 66.53
Plasticizer 23.4
Compatibilizer 10
Stabilizer 0.5
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After the DVA film was co-extruded as a film, the
residual plasticizer was removed via a heating operation
as discussed above to produce a DVA film free of residual
plasticizer/oils on the surfaces of the film.
[0089] Adhesive tie layer compositions and an
exemplary carcass compound were prepared as described
above for conventional elastomer compounding. The
compositions are set forth in Table 4 below. All
component amounts in Table 4 are parts per hundred rubber
(phr).
TABLE 4
Compound Ti T2 T3 T4 Carcass
BIIR 100. 100. 100. 100.
00 00 00 00
NR 70
SBR 30
N660 60.0 60.0 -- 60
0 0
N351 -- 40.0 40.0
0 0
Flectol 1
Process Oil 8.00 8.00 -- 10
Struktol 40MS 7.00 -- 4.00 4.00
St-acid 1.00 2.00 2.00 2.00 2
ZnO 1.00 3.00 3.00 3.00 3
MBTS 1.25 1.50 1.50 1.50
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TABLE 4 Cont.
Compound Ti T2 T3 T4 Carcass
Sulfur 0.50 0.50 0.50 0.50 2
Ti 4.00 -- 5.00 5.00 5
T2 -- 2.00 2.00
T3 -- 6.00 -- 6.00
T4 -- 6.00 6.00 6.00
Total 4.00 12.0 13.0 19.0 5.00
tackifiers, phr 0 0 0
Properties
Tensile Strength 9.69 8.64 11.3 11.0
3 1
Elongation 800 778 718 792
300% Modulus 2.88 3.53 3.72 3.58
Shore A 47 55 55 63
Tear Resistance 48.5 47.5 57.3 57.3
5 3 9 3
Peel Adhesion / Resistance N/mm
To Self 0.37 1.09 0.11 0.73
To DVA film 13.5 11.2 7.76 8.64
1 0
To ply compound 19.0 19.0 18.9 20.2
4 3 6 5
[0090] All of the adhesive tie layers showed an
excellent adhesion to the treated DVA layer when directly
bonded to the DVA film. In the peel adhesion testing, as
the amount of tackifier in the adhesive tie layer
increased, the bond between the adhesive tie layer and
the DVA film actually decreased, while the bond between
the adhesive tie layer and the ply compound was
relatively comparable for all of the adhesive
compositions. In comparison to other DVA laminate
constructions, such as those disclosed in U.S. Patent
Application 2008/314492, the above data shows that it is
not necessary to employ multiple tackifiers in the tie
gum layer, even in the absence of a thin film adhesive
layer, if the DVA is treated to remove residual
plasticizer/oils.
[0091] Thus, in accordance with the present invention,
it is not required to use a thin film adhesive layer
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between the DVA film and the tie gum layer to achieve
excellent adhesion for a DVA containing laminate.
Removal of the residual plasticizer and/or oils from the
DVA film permits the adhesive tie layer to bond more
readily with the DVA film and thereby improved adhesion
of the DVA film in an article. More particularly, due to
improved adhesion tires containing the bonded, treated
DVA film will have improved durability.
