U.S. patent application number 10/022108 was filed with the patent office on 2003-06-19 for method of improving carbon black dispersion in rubber compositions.
This patent application is currently assigned to Bridgestone Corp.. Invention is credited to Bohm, Georg G. A., Hergenrother, William L., Lawson, David F., Rademacher, Christine M., Ramic, Anthony J., Sarkar, Sunil B., Ulmer, James D..
Application Number | 20030111770 10/022108 |
Document ID | / |
Family ID | 21807853 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030111770 |
Kind Code |
A1 |
Bohm, Georg G. A. ; et
al. |
June 19, 2003 |
Method of improving carbon black dispersion in rubber
compositions
Abstract
A method for forming a vulcanizable composition of matter, the
method comprising providing a polymer cement or latex comprising at
least one rubber, adding at least one processing aid to the cement
or latex to form a modified rubber cement or latex, isolating the
rubber and at least one processing aid to form a premix, and mixing
the premix with carbon black.
Inventors: |
Bohm, Georg G. A.; (Akron,
OH) ; Ramic, Anthony J.; (Brook Park, OH) ;
Ulmer, James D.; (Akron, OH) ; Hergenrother, William
L.; (Akron, OH) ; Rademacher, Christine M.;
(Akron, OH) ; Lawson, David F.; (Uniontown,
OH) ; Sarkar, Sunil B.; (Akron, OH) |
Correspondence
Address: |
John H. Hornickel
Senior I. P. Counsel
Bridgestone/Firestone, Inc.
1200 Firestone Parkway
Akron
OH
44317
US
|
Assignee: |
Bridgestone Corp.
|
Family ID: |
21807853 |
Appl. No.: |
10/022108 |
Filed: |
December 13, 2001 |
Current U.S.
Class: |
264/349 ;
264/326; 523/351 |
Current CPC
Class: |
C08J 3/203 20130101;
Y10S 152/905 20130101; C08J 2321/00 20130101; C08J 3/215
20130101 |
Class at
Publication: |
264/349 ;
523/351; 264/326 |
International
Class: |
C08L 001/00; B29C
035/00 |
Claims
What is claimed is:
1. A method for forming a vulcanizable composition of matter, the
method comprising: providing a polymer cement or latex comprising
at least one rubber; adding at least one processing aid to the
cement or latex to form a modified rubber cement or latex;
isolating the rubber and at least one processing aid to form a
premix; and mixing the premix with carbon black.
2. The method of claim 1, where said step of adding at least one
processing aid to the cement or latex includes forming a cocktail,
which includes the processing aid and a solvent, and adding the
cocktail to the cement or latex.
3. The method of claim 2, where said step of forming the cocktail
includes heating the processing aid and solvent to a temperature of
from about 30 to about 140.degree. C.
4. The method of claim 3, where said step of forming the cocktail
includes combining the processing aid and solvent with an oil.
5. The method of claim 4, where the cocktail includes from about 10
to about 50 parts by weight processing aid, from about 100 to about
35 parts by weight solvent, and from about 0 to about 65 parts by
weight oil.
6. The method of claim 1, where said step of adding at least one
processing aid to the cement or latex includes forming a cocktail,
which includes the processing aid and an oil, and adding the
cocktail to the cement or latex.
7. The method of claim 1, where said step of isolating includes
drying the rubber and processing agent.
8. The method of claim 1, where said step of mixing occurs within a
mixer having a net mixing chamber volume of at least about 75 L
operated at a fill factor of at least about 50.
9. The method of claim 1, where the at least one processing aid is
a polar organic compound, a resin, a low molecular weight polymer,
or a mixture thereof.
10. The method of claim 9, where the polar organic compound is a
high-HLB surfactant, an ester, a ketone, an aldehyde, an ether, an
amide, an amine, a carboxylic acid, a fatty acid, a sulfonic acid,
an organic sulfate, a metal carboxylate, a metal sulfonate, or a
mixture thereof.
11. The method of claim 10, where the fatty acid salt includes a
mixture of zinc fatty acid salts.
12. The method of claim 1, where the rubber is a functionalized
rubber.
13. The method of claim 12, where the functionalized rubber is
prepared by anionically polymerizing conjugated dienes, alone or in
combination with vinyl aromatic monomers, and where the
polymerization is initiated with a cyclic amine initiator or a
tin-lithio initiator.
14. The method of claim 12, where the functionalized rubber is
prepared by terminating a polymerization with a coupling or
functional terminating agent.
15. The method of claim 12, where the functionalized rubber
includes both head and tail functionalization.
16. The method of claim 1, further comprising the step of shaping
the vulcanizable composition of matter into a green tire component,
and further comprising the step of curing the tire component.
17. The method of claim 1, where said step of adding at least one
processing aid includes adding from about 0.1 to about 15 parts by
weight processing aid per 100 parts by weight rubber.
18. The method of claim 1, where said step of adding at least one
processing aid includes adding from about 0.5 to about 12 parts by
weight processing aid per 100 parts by weight rubber.
19. A tire tread prepared by a method comprising: preparing a
vulcanizable composition of matter by providing a rubber cement or
latex comprising at least one rubber, adding at least one
processing aid to the rubber cement or latex to form a modified
rubber cement or latex, isolating the rubber and at least one
processing aid to form a premix, mixing the premix with carbon
black; shaping the vulcanizable composition of matter into a green
tire tread, and curing the tire tread.
20. A method for increasing the dispersion of carbon black within a
carbon-black filled tire component, the method comprising:
providing a rubber cement or latex comprising at least one rubber;
adding at least one processing aid to the rubber cement or latex to
form a modified rubber cement or latex; isolating the rubber and at
least one processing aid from the solvent to form a premix; and
mixing the premix with carbon black.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a process for improving carbon
black dispersion within carbon black-filled rubber
compositions.
BACKGROUND OF THE INVENTION
[0002] Carbon black is used as a filler within vulcanizable rubber
compositions of matter that are used to make tire components and
other rubber articles. The degree of carbon black dispersion within
these compositions ultimately impacts the properties of the tire or
other rubber articles. For example, higher dispersion results in
increased abrasion resistance.
[0003] Carbon black is typically added to these rubber compositions
during compounding, which is a process that includes mixing of
rubber, filler, and other compound components. During mixing,
processing aids have been added to improve the degree of carbon
black dispersion.
[0004] Despite the use of these conventional processing aides,
further improvement in carbon black dispersion is desired. This is
especially true where a large volume of rubber is compounded within
a large-scale mixing apparatus.
SUMMARY OF THE INVENTION
[0005] In general the present invention provides a method for
forming a vulcanizable composition of matter, the method comprising
providing a polymer cement or latex comprising at least one rubber,
adding at least one processing aid to the cement or latex to form a
modified rubber cement or latex, isolating the rubber and at least
one processing aid to form a premix, and mixing the premix with
carbon black.
[0006] The present invention further provides a tire tread prepared
by a method comprising preparing a vulcanizable composition of
matter by providing a rubber cement or latex comprising at least
one rubber, adding at least one processing aid to the rubber cement
or latex to form a modified rubber cement or latex, isolating the
rubber and at least one processing aid to form a premix, mixing the
premix with carbon black, shaping the vulcanizable composition of
matter into a green tire tread, and curing the tire tread.
[0007] The present invention also provides a method for increasing
the dispersion of carbon black within a carbon-black filled tire
component, the method comprising providing a rubber cement or latex
comprising at least one rubber, adding at least one processing aid
to the rubber cement or latex to form a modified rubber cement or
latex, isolating the rubber and at least one processing aid from
the solvent to form a premix, and mixing the premix with carbon
black.
[0008] This invention advantageously improves the dispersion of
carbon black within vulcanizable compositions that are compounded
in large volumes within large-scale mixing equipment. Among other
advantages, this increased carbon black dispersion allows for the
production of tire treads that exhibit improved wear.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0009] The vulcanizable rubber compositions, which are useful in
preparing tire components and other rubber articles, are prepared
by mixing a rubber/processing aid premix with carbon black. The
premix is prepared by adding at least one processing aid to a
polymer cement or aqueous latex, and subsequently removing the
solvent.
[0010] Polymer cements include a solution of at least one rubbery
elastomer in an organic solvent. The rubbery elastomers may be
dissolved or suspended in the organic solvent. The cement may also
be oil extended, which refers to a rubber cement that includes one
or more oils, such as aromatic and naphthenic oils, which are
typically employed in the rubber industry. Aqueous lattices include
suspensions of at least one rubbery elastomer. These lattices may
also be oil extended.
[0011] Rubbery elastomers include natural and synthetic elastomers.
The synthetic elastomers typically derive from the polymerization
of conjugated diene monomers. These conjugated diene monomers may
be copolymerized with other monomers such as vinyl aromatic
monomers. Other rubbery elastomers may derive from the
polymerization of ethylene together with one or more
.alpha.-olefins and optionally one or more diene monomers.
[0012] Useful rubbery elastomers include natural rubber, synthetic
polyisoprene, polybutadiene, polyisobutylene-co-isoprene, neoprene,
poly(ethylene-co-propylene), poly(styrene-co-butadiene),
poly(styrene-co-isoprene), and
poly(styrene-co-isoprene-co-butadiene),
poly(isoprene-co-butadiene), poly(ethylene-co-propylene-co-diene),
polysulfide rubber, acrylic rubber, urethane rubber, silicone
rubber, epichlorohydrin rubber, and mixtures thereof. These
elastomers can have a myriad of macromolecular structures including
linear, branched and star shaped.
[0013] The synthetic elastomers include functionalized elastomers.
These elastomers preferably contain at least one functional group
that will react or interact with a rubber filler. These functional
groups may be located either at the end of the polymer chain or
pendent to the polymer backbone. Those functional groups that are
pendant to the polymer chain are preferably located near the end of
the chain. Useful techniques for preparing functionalized
elastomers are well known in the art. For example, these functional
groups can be added to the polymer during synthesis of the
elastomer or by grafting to the elastomer.
[0014] In one embodiment, the elastomers are synthesized by using
anionic polymerization initiators that include cyclic amine groups,
which impart a cyclic amine functionality to the resulting
polymers. An example of these initiators includes lithio
hexamethyleneimine, which is disclosed in U.S. Pat. Nos. 6,080,835;
5,786,441; 6,025,450; and 6,046,288, which are incorporated herein
by reference.
[0015] In another embodiment, the elastomers are synthesized by
using anionic polymerization initiators that include at least one
tin atom. These compounds, such as tin-lithium initiators, are
believed to incorporate a tin atom at the head of the polymer
chain. An example includes tributyltin lithium, which is disclosed
in U.S. Pat. No. 5,268,439, which is incorporated herein by
reference.
[0016] In yet another embodiment, anionically-polymerized
elastomers, whether head-functionalized or not, are terminated with
a coupling agent or a terminating agent that will impart an end
functionality to the polymer. Useful compounds that may be used to
couple or functionalize the tail end of the living polymers
include, but are not limited to, those compounds that can be
defined by the formula R.sub.nMX.sub.4-n, where R is an organic
group, M is silicon or tin, X is a halogen atom, and n is a numeral
from 0 to 3. Preferably, R is a simple alkyl group having from 1 to
about 10 carbon atoms. Exemplary compounds include SnCl.sub.4,
R.sub.2SnCl.sub.2, and RSnCl.sub.3, which are disclosed in U.S.
Pat. No. 5,332,810, which is incorporated herein by reference.
Other compounds that may be used alone or in conjunction with the
foregoing tin or silicon compounds include metal halides, metalloid
halides, alkoxysilanes, imine-containing compounds, esters,
ester-carboxylate metal complexes, alkyl ester carboxylate metal
complexes, aldehydes or ketones, amides, isocyanates,
isothiocyanates, imines, and epoxides.
[0017] In still another embodiment, elastomers synthesized with
coordination catalyst systems, such as lanthanide-based catalyst
systems, are terminated with a coupling agent or terminating agent
that will impart an end functionality to the polymer. Useful
coupling or functionalizing agents include those described above,
which are described in International Application Nos.
PCT/US00/30743 and PCT/US00/30875, which are incorporated herein by
reference.
[0018] The rubbery elastomers generally have a number average
molecular weight from about 60,000 to about 500,000 g/mol,
preferably from about 100,000 to about 400,000 g/mol, and more
preferably from about 120,000 to about 300,000 g/mol, as determined
by using gel permeation chromatography (GPC) calibrated with
polystyrene standards and adjusted for the Mark-Houwink constants
for the polymer in question.
[0019] In preparing the polymer cements, suitable types of organic
solvents include, but are not limited to, aliphatic,
cycloaliphatic, and aromatic hydrocarbons. Some representative
examples of these solvents include n-pentane, n-hexane, n-heptane,
n-octane, n-nonane, n-decane, isopentane, isohexane, isoheptane,
isooctane, 2,2-dimethyl butane, petroleum ether, kerosene,
petroleum spirits, and isomers thereof. Some representative
examples of suitable cycloaliphatic solvents include cyclopentane,
cyclohexane, methylcyclopentane, methyl cyclohexane, and the like.
Some representative examples of suitable aromatic solvents include
benzene, toluene, xylene, ethyl benzene, diethyl benzene,
mesitylene, and mixtures of aliphatic, cycloaliphatic and aromatic
compounds. Commercial mixtures of the above hydrocarbons, such as
hexanes, may also be used. For environmental reasons, aliphatic and
cycloaliphatic solvents are highly preferred.
[0020] Preferably, the polymer cement or aqueous latex includes
from about 5 to about 60 percent by weight elastomer, more
preferably from about 10 to about 35 percent by weight elastomer,
and even more preferably from about 15 to about 25 percent by
weight elastomer.
[0021] The polymer cement may be prepared by using several
techniques. In one embodiment, the cement is prepared by
synthesizing elastomers within an organic solvent. In another
embodiment, the cement is prepared by dissolving or suspending the
elastomers within an organic solvent.
[0022] The aqueous latex can be obtained from natural sources or
synthetically prepared. Synthetically, rubbery elastomers can be
synthesized by well-known techniques such as emulsion
polymerization. Or, one or more rubbery elastomers can be
emulsified by using, for example, emulsifiers or surfactants and a
high shear colloidal mill.
[0023] Processing aids include those compounds, or mixtures
thereof, that aid in the dispersion of filler. Typically, these
compounds improve the dispersion of filler particles, such as
carbon black, within rubber compositions. They may react or
interact with the filler and thereby facilitate the filler's
dispersion, or they may facilitate filler incorporation and speed
the attainment of filler dispersion. Useful processing aids include
polar organic compounds, resins, and low-molecular weight polymers.
Petroleum-derived oils, such as paraffinic, aromatic, and
naphthenic oils, are preferably excluded. Those compounds having a
flash-point that is less than about 125.degree. C. are preferably
excluded.
[0024] The polar organic compounds preferably include high-HLB
surfactants, esters, ketones, aldehydes, ethers, amides, amines,
carboxylic acids, fatty acids, sulfonic acids, organic sulfates,
metal carboxylates, metal sulfonates, and mixtures thereof.
[0025] The preferred high-HLB surfactants include those compounds
that have a hydrophilic-lipophilic balance (HLB) from about 3 to
about 35, more preferably from about 10 to about 33, and even more
preferably from about 20 to about 30. Higher HLB values correspond
to greater hydrophilicity. These surfactants may be liquid or solid
at room temperature. The molecular weight of these surfactants is
preferably from about 100 g/mole to about 15,000 g/mole, more
preferably from about 1,000 g/mole to about 14,000 g/mole and more
preferably from about 5,000 g/mole to about 13,000 g/mole.
[0026] Useful high-HLB surfactants are commercially available under
the tradenames Tween 20, Span 20, Span 60, and Myrj 59 (ICI
Surfactants; Wilmington, Del.), and the tradenames Pluronic L35,
Pluronic F38, and Pluronic F88 (BASF; Mount Olive, N.J.).
[0027] The carboxylic acids, which may be saturated or unsaturated,
preferably include those containing from 2 to about 30 carbon
atoms, more preferably about 5 to about 24 carbon atoms, and even
more preferably about 8 to about 18 carbon atoms. Preferred acids
include fatty acids, which are those carboxylic acids that are
obtained from natural sources.
[0028] Useful acids include stearic acid, lauric acid, palmitic
acid, oleic acid, myristic acid, and linoleic acid.
[0029] The sulfonic acids include those compounds that include one
or more sulfonic acid groups (SO.sub.2OH) that are attached to a
carbon atom of a hydrocarbyl group.
[0030] Exemplary types of sulfonic acids include alkylsulfonic
acids, alkylbenzenesulfonic acids, and alkylnaphthalenesulfonic
acids. Useful sulfonic acids include octylsulfonic acid,
dodecylbenzenesulfonic acid, and dodecylnaphthenesulfonic acid.
[0031] The carboxylates, which may also be referred to as organic
salts, preferably include alkali metals such as sodium and
potassium, alkaline-earth metals such as magnesium and calcium, or
transition metals such as iron, nickel, and zinc. The hydrocarbon
portion of these carboxylates preferably derives from carboxylic
acids, which may be saturated or unsaturated, that include from
about 4 to about 40 carbon atoms, more preferably from about 6 to
about 30 carbon atoms, and most preferably from about 8 to about 24
carbon atoms. These hydrocarbons are preferably aliphatic, and even
more preferably saturated. In one embodiment, the hydrocarbon
derives from a fatty acid, examples of which are described
above.
[0032] Examples of organic salts include sodium stearate, sodium
myristate, sodium laurate, sodium palmitate, sodium oleate, sodium
linoleate, calcium stearate, calcium myristate, calcium laurate,
calcium palmitate, calcium oleate, sodium myristate, zinc stearate,
zinc myristate, zinc laurate, zinc palmitate, zinc oleate, and zinc
linoleate.
[0033] Useful organic salts are commercially available under the
tradename AKROCHEM PROAID 9810 (Akrochem; Akron, Ohio), NORAC
Calcium Stearate (Sovereign Chemical Co.; Akron, Ohio), COAD 10,
20, 23, LM, which are calcium stearate, zinc stearate, zinc
stearate, and calcium stearate salts, respectively (Sovereign
Chemical Co.), MAXIFLOW RS and SP (Rubber Service; Argentina),
STRUKTOL A50, A91F, and EF44A, which are zinc soaps of various
fatty acids (Struktol; Stow, Ohio). Blends of fatty acids together
with esters are also commercially available under the tradename
STRUKTOL WA48 and WB16 (Struktol).
[0034] In a preferred embodiment, blends of zinc carboxylates are
employed. These blends may include mixtures of carboxylates that
are distinguished based upon the configuration of the hydrocarbon
or the size of the hydrocarbon. These blends preferably include
mixtures of various zinc fatty acid salts.
[0035] Useful blends of zinc carboxylates are commercially
available under the tradename Aktiplast GT (Rhein Chemie Corp;
Trenton, N.J.), which are zinc fatty acid salts.
[0036] The metal sulfonates preferably include alkali metals such
as sodium and potassium, alkaline-earth metals such as magnesium
and calcium, or transition metals such as iron, nickel, and zinc.
The hydrocarbon portion of these carboxylates preferably derives
form sulfonic acids that include from about 4 to about 40 carbon
atoms, more preferably from about 6 to about 30 carbon atoms, and
most preferably from about 8 to about 24 carbon atoms. These
hydrocarbons are preferably aliphatic, and even more preferably
saturated.
[0037] Useful types of metal sulfonates include sodium, calcium or
zinc alkyl sulfonate, alkylbenzenesulfonate, and alkylnaphthalene
sulfonate.
[0038] Organic sulfates are metal salts of the reaction product of
sulfuric acid and an alcohol. Alkali metals, alkaline-earth metals,
and transition metals may be employed to form the salt. The alcohol
preferably includes from about 2 to 30 carbon atoms and more
preferably from about 6 to about 20 carbon atoms.
[0039] Examples of organic sulfates include sodium laurylsulfate,
calcium stearyl sulfate, zinc oleyl sulfate, and sodium
dodecylbenzenesulfonate.
[0040] Useful low molecular weight polymers include those polymers
that preferably have a number average molecular weight from about
1,000 g/mol to about 60,000 g/mol, more preferably from about 2,000
g/mol to about 50,000 g/mol, and even more preferably from about
3,000 g/mol to about 45,000 g/mol.
[0041] Preferred polymers derive from the polymerization of
alpha-olefins, dienes, conjugated dienes, fluorine-containing
monomers, or combinations thereof. Examples of useful low-molecular
weight polymers include polyethylene, polypropylene, polybutene,
polybutylene, ethylene-propylene rubber, ethylene-propylene-diene
rubber, polytetrafluoroethylene, polyisoprene, and depolymerized
natural rubber.
[0042] Resins generally refer to those compounds that will
self-react to form larger compounds. Many of these compounds are
low-melting temperature solids.
[0043] Exemplary resins include pine tar resins, low molecular
weight unsaturated polyesters, phenol formaldehyde, and melamine
formaldehyde.
[0044] The premix is formed by adding at least one processing aid
to the polymer cement or aqueous latex, which thereby forms a
modified polymer cement or latex, and subsequently isolating the
rubbery elastomer and processing aid from the solvent of the cement
or latex. The addition of the processing aid can occur by employing
several techniques. In one embodiment, the processing aid is added
directly to the cement or latex. In another embodiment, the
processing aid is added to the cement or latex via a cocktail. Once
the processing aid is added to the cement or latex to form the
modified polymer cement, the modified polymer cement or latex may
be mixed or agitated. The polymer and processing aid are then
isolated from the solvent and optionally dried to form the
premix.
[0045] In one embodiment, the cocktail is a blend of an organic
solvent and a processing aid. Additional ingredients that may be
added to this cocktail include antioxidants and oils, which include
plasticizers, extender oils, and synthetic oils. Useful organic
solvents are described above. The preferred solvent includes
commercial cyclohexanes, commercial hexanes, or a blend of
commercial cyclohexanes and hexanes.
[0046] In another embodiment, the cocktail is a blend of a
processing oil and a processing aid. Preferred processing oils
include those oils that are typically employed to extend cements of
rubbery elastomers. These oils include paraffinic, aromatic and
naphthenic oils.
[0047] Where the cocktail includes a solvent, a processing aid, and
optional oil, the cocktail preferably includes from about 10 to
about 50 parts by weight processing aid, from about 100 to about 35
parts by weight solvent, and from about 0 to about 65 parts by
weight oil, where the solvent and oil total 100 parts by weight.
More preferably, the cocktail includes from about 15 to about 45
parts by weight processing aid, from about 95 to about 45 parts by
weight solvent, and from about 5 to about 55 parts by weight oil,
where the solvent and oil total 100 parts by weight.
[0048] Where the cocktail includes a processing aid and oil, the
cocktail preferably includes from about 15 to about 55, and more
preferably from about 20 to about 45 parts by weight processing aid
per 100 parts by weight oil.
[0049] The cocktail is prepared by combining and preferably mixing
the ingredients. This step of combining preferably occurs at a
temperature from about 30 to about 140.degree. C., more preferably
from about 40 to about 130.degree. C., and even more preferably
from about 50 to about 120.degree. C. Mixing is preferably
continued until the processing aid is homogenized within the
solvent and optional oil.
[0050] The cocktail is preferably added to the polymer cement while
the polymer cement is undergoing agitation. Preferably, the polymer
cement is at a temperature of about 30 to about 120.degree. C.,
more preferably from about 40 to about 110.degree. C., and even
more preferably from about 50 to about 100.degree. C. The cocktail
is also preferably maintained within these temperature ranges
during the addition process.
[0051] The amount of processing aid added to the polymer cement or
latex is generally from about 0.1 to about 15 phr, preferably from
about 0.5 to about 12 phr, more preferably from about 1.0 to about
10 phr, still more preferably from about 1.2 to about 8 phr, and
still more preferably from about 1.5 to about 5 phr, where phr
refers to the parts by weight of ingredient, i.e., processing aid,
per 100 parts by weight rubber.
[0052] After formation of the modified polymer cement or latex, the
rubbery elastomer, the processing aid, and other optional additives
such as oil, are isolated from the solvent and preferably dried.
This isolated composition may be referred to as the
rubber/processing aid premix or simply premix. Conventional
procedures for desolventization and drying may be employed. In one
embodiment, where a polymer cement is employed, the premix may be
isolated from the solvent by steam distillation of the solvent
followed by filtration. Residual solvent may be removed by drying
the rubber/processing aid masterbatch by using conventional drying
techniques such as a drum dryer. Alternatively, the rubber-modified
cement may be directly drum dried to produce the premix. In another
embodiment, where an aqueous latex is employed, the premix can be
isolated by coagulation, which is a technique that is known in the
art. These techniques may employ compounds such as calcium chloride
or other salts that serve to destabilize the emulsion.
[0053] In preparing the vulcanizable compositions of matter, the
rubber/processing aid premix and at least one filler are combined
and mixed or compounded. Other ingredients that are typically
employed in rubber compounding may also be added.
[0054] The rubber compositions may include fillers such as
inorganic and organic fillers. The organic fillers include carbon
black. The inorganic fillers may include silica, aluminum
hydroxide, magnesium hydroxide, clays (hydrated aluminum
silicates), and mixtures thereof.
[0055] A multitude of rubber curing agents may be employed. For
example, sulfur or peroxide-based curing systems may be employed.
Also, see Kirk-Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY,
3.sub.rd Edition, Wiley Interscience, N.Y. 1982, Vol. 20, pp.
365-468, particularly VULCANIZATION AGENTS AND AUXILIARY MATERIALS
pp. 390-402, or Vulcanization by A. Y. Coran, ENCYCLOPEDIA OF
POLYMER SCIENCE AND ENGINEERING, 2.sub.nd Edition, John Wiley &
Sons, Inc., 1989, which are incorporated herein by reference.
Vulcanizing agents may be used alone or in combination.
[0056] Other ingredients that may be employed include accelerators,
oils, waxes, scorch inhibiting agents, processing aids, zinc oxide,
tackifying resins, reinforcing resins, fatty acids such as stearic
acid, peptizers, and one or more additional rubbers.
[0057] Fillers are typically employed in an amount from about 1 to
about 100 phr, and preferably from about 20 to about 90 phr, and
more preferably from about 35 to about 80 phr, where phr refers to
parts by weight ingredient per 100 parts by weight rubber within
the compound, which may include the rubber within the premix as
well as any additional rubber that may be added during
compounding.
[0058] The vulcanizable compositions of matter prepared according
to this invention are mixed in conventional large-scale mixing
equipment. This equipment is generally characterized by having a
net mixing chamber volume of at least about 75 L, advantageously at
least about 270 L, and more advantageously at least about to 620 L.
Examples of these mixers include Banbury mixers. Typically, these
mixers operate at a fill factor of at least about 50,
advantageously at least about 60, and more advantageously at least
about 70.
[0059] Preferably, the vulcanizable rubber composition is prepared
by forming an initial masterbatch that includes the premix and
filler. This initial masterbatch is mixed at a starting temperature
of from about 25.degree. C. to about 100.degree. C. with a
discharge temperature of about 135.degree. C. to about 180.degree.
C. To prevent premature vulcanization (also known as scorch), this
initial masterbatch generally excludes any vulcanizing agents. Once
the initial masterbatch is processed, the vulcanizing agents are
introduced and blended into the initial masterbatch at low
temperatures in a final mix stage, which does not initiate the
vulcanization process. Optionally, additional mixing stages,
sometimes called remills, can be employed between the masterbatch
mix stage and the final mix stage. Rubber compounding techniques
and the additives employed therein are generally known as disclosed
in the in The Compounding and Vulcanization of Rubber, by Stevens
in RUBBER TECHNOLOGY SECOND EDITION (1973 Van Nostrand Reinhold
Company). The mixing conditions and procedures applicable to
silica-filled tire formulations are also well known as described in
U.S. Pat. Nos. 5,227,425; 5,719,207; 5,717,022, as well as EP
0890606, all of which are incorporated herein by reference.
[0060] Where the vulcanizable rubber compositions are employed in
the manufacture of tires, these compositions can be processed into
tire components according to ordinary tire manufacturing techniques
including standard rubber shaping, molding and curing techniques.
Typically, vulcanization is effected by heating the vulcanizable
composition in a mold; e.g., it is heated to about 170.degree. C.
Cured or crosslinked rubber compositions may be referred to as
vulcanizates, which generally contain three-dimensional polymeric
networks that are thermoset. The other ingredients, such as
processing aides and fillers, are generally evenly dispersed
throughout the vulcanized network. Tire components of this
invention preferably include tire treads. The rubber compositions,
however, can also be used to form other elastomeric tire components
such as subtreads, sidewalls, body ply skims, bead fillers and the
like. Pneumatic tires can be made as discussed in U.S. Pat. Nos.
5,866,171; 5,876,527; 5,931,211; and 5,971,046, which are
incorporated herein by reference.
[0061] The vulcanizable rubber compositions prepared according to
this invention may also be employed in the manufacture of other
rubber articles. For example, they may be employed in the
manufacture of rubber air springs, which are vibration damping
devices that are typically employed in trucks. They may also be
employed in manufacture of rubber sheeting and other articles that
are employed in preparing roofing materials.
[0062] In order to demonstrate the practice of the present
invention, the following examples have been prepared and tested.
The examples should not, however, be viewed as limiting the scope
of the invention. The claims will serve to define the
invention.
EXAMPLES
[0063] Experiment I
[0064] Two rubber formulations were prepared according to the
recipe in Table I.
1 TABLE I Formulation A B Masterbatch Ingredients Functionalized
and oil-extended poly(styrene- 77.42 -- co-butadiene)
Functionalized and oil-extended poly(styrene- -- 80.5
co-butadiene)/processing aid premix Natural Rubber 30.00 30.00
Carbon Black 41.00 41.00 Wax 1.00 1.00 Antiozonant 0.95 0.95 Zinc
Oxide 2.50 2.50 Stearic Acid 2.00 2.00 Processing Aid 3.00 -- Final
Mix Ingredients Sulfur 1.30 1.30 N,N-Dicyclohexyl-2-benzothiazole
1.70 1.70 sulfonamide N,N-Diphenyl guanidine 0.20 0.20
[0065] These formulations were mixed in a Banbury internal mixer
having a net mixing chamber volume of about 75 L loaded to a fill
factor of about 70.
[0066] The oil-extended functionalized poly(styrene-co-butadiene)
was prepared by polymerizing styrene and butadiene monomer with
hexamethyleneimine as an initiator in the presence of hexanes and
terminated with a mixture of tributyltin chloride and tin
tetrachloride as described in U.S. Pat. No. 5,332,810. The polymer
was characterized by having about 27% by weight styrene content and
a glass transition temperature of about -46.degree. C. The polymer
was oil extended by using an aromatic process oil to achieve 7.42
parts by weight oil and 70 parts by weight polymer. The processing
aid was a mixture of zinc fatty acid salts obtained under the
tradename Aktiplast GT (Rhein Chemie).
[0067] In preparing formulation A, the processing aid was added
directly to the masterbatch during initial mixing within the
Banbury mixer. In other words, it was added during solid-state
mixing. In preparing formulation B, the processing aid was not
added during solid state mixing. Instead, a premix was prepared
according to the practice of this invention. Specifically, a
cocktail containing 12% by weight zinc fatty acid salts was
prepared by adding Aktiplast GT (Rhein Chemie) to cyclohexanes and
heated to about 66.degree. C. This cocktail, which was maintained
at about 66.degree. C., was then added to a cement of the
oil-extended functionalized poly(styrene-co-butadiene) in hexanes.
This cement contained about 1.7% by weight oil and about 15.7% by
weight polymer, with the remainder being commercial hexanes. The
resultant modified cement, at about 60-95.degree. C., was agitated
and directly drum dried to form the premix, which contained about
4.3 parts by weight of the zinc fatty acid salts, about 10.7 parts
by weight oil, and 100 parts by weight rubber.
[0068] The mixing included three stages as set forth in Table
II.
2TABLE II Step 1 2 3 4 Masterbatch Chamber Temp. (.degree. C.)
66-68 -- 165 165-168 Circulating Water Temp. (.degree. C.) 66 66 66
66 Rotor Speed (RPM) 65 65 65 65 Cumulative Mix Time (sec) 0 30 --
.about.99-105 Action Add polymers, carbon black, pigments Add
stearic acid Mix to 165.degree. C. Drop batch Remill Chamber Temp.
(.degree. C.) 53-60 135 135-138 -- Circulating Water Temp.
(.degree. C.) 43 43 43 -- Rotor Speed (RPM) 60 60 60 -- Cumulative
Mix Time (sec) 0 -- .about.62-72 -- Action Add masterbatch stock
Mix to 135.degree. C. Drop batch -- Final Chamber Temp. (.degree.
C.) 43-49 93 93-96 -- Circulating Water Temp. (.degree. C.) 43 43
43 -- Rotor Speed (RPM) 40 40 40 -- Cumulative Mix Time (sec) 0 --
.about.67-78 -- Action Add remill stock and Mix to 93.degree. C.
Drop batch -- curatives
[0069] The final mix or compound was analyzed for Mooney Scorch
according to ASTM D 1646 (1999). The compounds were also analyzed
for Mooney Viscosity (ML.sub.1+4@130.degree. C.). The results of
these tests are set forth in Table III.
[0070] Test specimens of each rubber formulation were prepared by
cutting out the required mass from an uncured sheet (about 2.5 mm
to 3.81 mm thick). Test specimens were cured within closed cavity
molds under pressure for 13 minutes at 165.degree. C. Modulus at
300% and tensile strength were measured according to ASTM D 412
(1998) Method B, where samples were died from a cured sheet about
1.8 mm thick. Rubber cylinders measuring about 9.5 mm in diameter
and 16 mm high were analyzed by using a Dynastat viscoelastic
analyzer and an RDA (Reometrics Dynamic Analyzer). Dynastat M', RDA
G', and Dynastat tan 6 are reported in Table III. Carbon black
dispersion (Surfanalyzer Dispersion Index) was measured according
to ASTM D 2663, Test Method C (1995), except that the same
calibration values, A and B, were used for all test samples with
periodic review of the calculated dispersion ratings relative to
dispersion estimates from light optical microscopy. Where carbon
black dispersion was measured for the masterbatch stage or the
remill stage, the test specimens were cured by using electron beam
irradiation. Test specimens formed into rubber wheels of about 48
mm in outside diameter, about 22 mm in inside diameter, and about
4.8 mm in thickness were subjected to the Lambourn abrasion test,
with Formulation A as the control. Pendulum rebound was analyzed by
employing a Zwick Rebound Resilience Tester (Zwick). The results of
the foregoing tests are reported in Table III.
3TABLE III Property A B Surfanalyzer Dispersion Index (Masterbatch
Stage) 43.5 59.6 Surfanalyzer Dispersion Index (Remill Stage) 54.1
71.7 Surfanalyzer Dispersion Index (Final Stage) 52.8 76.3 Mooney
Viscosity (ML.sub.1+4 @ 130.degree. C.) 56.8 58.9 Mooney Scorch
Time (min.) 20.0 20.4 Modulus @ 300% (23.degree. C.) (MPa) 9.053
8.778 Tensile Strength @ 23.degree. C. (MPa) 14.81 14.55 Elongation
@ Break (%) 400 403 Pendulum Rebound @ 50.degree. C. (%) 69.2 69.2
Lambourn Abrasion Resistance Index 100.0 109.6 Dynastat M' @
25.degree. C. (MPa) 6.26 6.14 Dynastat tan .delta. @ 50.degree. C.
0.090 0.092 25.degree. C. RDA G' @ 14% Strain (MPa) 1.84 1.82
[0071] Various modifications and alterations that do not depart
from the scope and spirit of this invention will become apparent to
those skilled in the art. This invention is not to be duly limited
to the illustrative embodiments set forth herein.
* * * * *