U.S. patent number 10,385,184 [Application Number 15/596,431] was granted by the patent office on 2019-08-20 for rubber composition and pneumatic tire comprising tread formed from said rubber composition.
This patent grant is currently assigned to SUMITOMO RUBBER INDUSTRIES, LTD.. The grantee listed for this patent is SUMITOMO RUBBER INDUSTRIES, LTD.. Invention is credited to Toshifumi Haba, Masaki Oshimo.
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United States Patent |
10,385,184 |
Haba , et al. |
August 20, 2019 |
Rubber composition and pneumatic tire comprising tread formed from
said rubber composition
Abstract
Provided is a rubber composition that achieves a balanced
improvement in fuel economy, abrasion resistance, and wet grip
performance while having good processability. Also provided is a
pneumatic tire including a tread formed from the rubber
composition. The present invention relates to a rubber composition
containing: a rubber component including a copolymer; and carbon
black and/or silica, the copolymer containing a structural unit
derived from a conjugated diene monomer and a structural unit
derived from a compound represented by the following formula (1):
##STR00001## wherein R.sup.11 represents a C1-C30 hydrocarbon
group.
Inventors: |
Haba; Toshifumi (Kobe,
JP), Oshimo; Masaki (Kobe, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO RUBBER INDUSTRIES, LTD. |
Kobe-shi, Hyogo |
N/A |
JP |
|
|
Assignee: |
SUMITOMO RUBBER INDUSTRIES,
LTD. (Kobe-Shi, Hyogo, JP)
|
Family
ID: |
59257945 |
Appl.
No.: |
15/596,431 |
Filed: |
May 16, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170355830 A1 |
Dec 14, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Jun 14, 2016 [JP] |
|
|
2016-118115 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F
236/06 (20130101); C08K 3/04 (20130101); C08L
9/00 (20130101); C08K 3/36 (20130101); C08F
218/10 (20130101); B60C 1/0016 (20130101); C08K
3/36 (20130101); C08L 31/02 (20130101); C08K
3/04 (20130101); C08L 31/02 (20130101); C08K
3/36 (20130101); C08L 9/00 (20130101); C08K
3/04 (20130101); C08L 9/00 (20130101); C08L
9/00 (20130101); C08K 3/04 (20130101); C08L
31/00 (20130101); C08K 3/04 (20130101); C08L
31/04 (20130101); C08K 3/04 (20130101) |
Current International
Class: |
C08K
3/04 (20060101); C08K 3/36 (20060101); C08F
236/06 (20060101); C08F 218/10 (20060101); B60C
1/00 (20060101); C08L 9/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Cai; Wenwen
Attorney, Agent or Firm: Birch, Stewart, Kolasch & Birch
LLP
Claims
The invention claimed is:
1. A pneumatic tire, comprising a tread formed from a rubber
composition, the rubber composition comprising: a rubber component
comprising a copolymer; and at least one of carbon black or silica,
the copolymer containing a structural unit derived from a
conjugated diene monomer and a structural unit derived from a
compound represented by the following formula (1): ##STR00008##
wherein R.sup.11 represents a C3-C30 hydrocarbon group.
2. The pneumatic tire according to claim 1, wherein the copolymer
contains, based on 100% by mass of structural units of the
copolymer, 5% to 95% by mass of the structural unit derived from a
conjugated diene monomer and 5% to 95% by mass of the structural
unit derived from a compound of formula (1).
3. The pneumatic tire according to claim 1, wherein the copolymer
has a weight average molecular weight of 5,000 to 2,000,000 and a
molecular weight distribution of 2.1 to 11.
4. The pneumatic tire according to claim 1, wherein the compound of
formula (1) is vinyl cinnamate.
5. The pneumatic tire according to claim 1, wherein the conjugated
diene monomer is 1,3-butadiene.
6. The pneumatic tire according to claim 1, wherein the copolymer
has at its end a functional group having an affinity for filler.
Description
TECHNICAL FIELD
The present invention relates to a rubber composition and a
pneumatic tire including a tread formed from the rubber
composition.
BACKGROUND ART
Tire treads are required to have high properties such as mainly
fuel economy, abrasion resistance, and wet grip performance.
Various techniques for improving these properties have been
studied.
For example, fuel economy is known to be improved by introducing a
functional group having an affinity for filler into a polymer chain
end. Abrasion resistance is known to be improved by using a high
molecular weight polymer having a molecular weight of 250,000 or
more. Wet grip performance is known to be improved by using a
polymer having a high glass transition temperature (Tg).
However, the introduction of a functional group having an affinity
for filler, the use of a high molecular weight polymer, and the use
of a polymer having a high Tg resulting from increased styrene
content all unfortunately increase the hardness of rubber
compositions, thereby deteriorating processability.
Patent Literature 1 discloses a tire rubber composition containing
a liquid resin having a softening point of -20.degree. C. to
45.degree. C. and a specific silica to improve fuel economy,
abrasion resistance, and wet grip performance. However, there is
still room for improvement to achieve a balanced improvement in
these properties while ensuring good processability.
CITATION LIST
Patent Literature
Patent Literature 1: JP 2013-053296 A
SUMMARY OF INVENTION
Technical Problem
The present invention aims to solve the above problem and provide a
rubber composition that achieves a balanced improvement in fuel
economy, abrasion resistance, and wet grip performance while having
good processability, and also provide a pneumatic tire including a
tread formed from the rubber composition.
Solution to Problem
The present invention relates to a rubber composition, containing:
a rubber component including a copolymer; and at least one of
carbon black or silica, the copolymer containing a structural unit
derived from a conjugated diene monomer and a structural unit
derived from a compound represented by the following formula
(1):
##STR00002## wherein R.sup.11 represents a C1-C30 hydrocarbon
group.
The copolymer preferably contains, based on 100% by mass of
structural units of the copolymer, 5% to 95% by mass of the
structural unit derived from a conjugated diene monomer and 5% to
95% by mass of the structural unit derived from a compound of
formula (1).
The copolymer preferably has a weight average molecular weight of
5,000 to 2,000,000 and a molecular weight distribution of 2.1 to
11.
The compound of formula (1) is preferably vinyl cinnamate.
The conjugated diene monomer is preferably 1,3-butadiene.
The copolymer preferably has at its end a functional group having
an affinity for filler.
The present invention also relates to a pneumatic tire, including a
tread that is formed from the rubber composition.
Advantageous Effects of Invention
The rubber composition of the present invention contains: a rubber
component including a copolymer that contains a structural unit
derived from a conjugated diene monomer and a structural unit
derived from a compound of formula (1); and carbon black and/or
silica. Such a rubber composition achieves a balanced improvement
in fuel economy, abrasion resistance, and wet grip performance
while having good processability.
DESCRIPTION OF EMBODIMENTS
The rubber composition of the present invention contains a rubber
component including a copolymer that contains a structural unit
derived from a conjugated diene monomer and a structural unit
derived from a compound of formula (1). The rubber composition also
contains carbon black and/or silica. When a copolymer containing a
structural unit derived from a conjugated diene monomer and,
further, a structural unit derived from a compound of formula (1)
is used together with carbon black and/or silica, the resulting
rubber composition shows good processability before vulcanization,
and further achieves a balanced improvement in fuel economy,
abrasion resistance, and wet grip performance. Thus, a rubber
composition excellent in the balance of these properties can be
provided.
The copolymer contains a structural unit derived from a conjugated
diene monomer. The conjugated diene monomer preferably has 4 to 8
carbon atoms, and examples include 1,3-butadiene, isoprene, and
2,3-dimethyl-1,3-butadiene. In view of fuel economy, abrasion
resistance, and wet grip performance, 1,3-butadiene or isoprene is
preferred among these, with 1,3-butadiene being more preferred.
These monomers may be used alone, or two or more of these may be
used in combination.
In the copolymer, the amount of the structural unit derived from a
conjugated diene monomer, based on 100% by mass of the structural
units of the copolymer, is preferably 5% by mass or more, more
preferably 30% by mass or more, still more preferably 50% by mass
or more, particularly preferably 60% by mass or more. The amount is
also preferably 95% by mass or less, more preferably 90% by mass or
less, still more preferably 80% by mass or less. When it is less
than 5% by mass, abrasion resistance may decrease. When it is more
than 95% by mass, fuel economy may decrease.
The copolymer contains a structural unit derived from a compound
represented by the formula (1) below. When the copolymer contains a
structural unit derived from a compound of formula (1) together
with the structural unit derived from a conjugated diene monomer,
preferably 1,3-butadiene, a balanced improvement in fuel economy,
abrasion resistance, and wet grip performance can be achieved while
ensuring good processability.
##STR00003##
In formula (1), R.sup.11 represents a C1-C30 hydrocarbon group.
Examples of the hydrocarbon group for R.sup.11 include aliphatic
hydrocarbon groups, alicyclic hydrocarbon groups, aromatic
hydrocarbon groups, and combinations of these hydrocarbon groups.
In order to better achieve the effects of the present invention,
the hydrocarbon group R.sup.11 preferably has 1 to 20 carbon atoms,
more preferably 3 to 16 carbon atoms, still more preferably 5 to 12
carbon atoms.
In order to better achieve the effects of the present invention,
R.sup.11 is preferably a group represented by --R.sup.12--R.sup.13
where R.sup.12 represents a C1-C20 aliphatic hydrocarbon group, and
R.sup.13 represents a C6-C10 aromatic hydrocarbon group.
The aliphatic hydrocarbon group for R.sup.12 preferably has 1 to 10
carbon atoms, more preferably 2 to 4 carbon atoms. Examples of the
aliphatic hydrocarbon group R.sup.12 include alkylene and
alkenylene groups, with alkenylene groups being more preferred.
Specific examples of the alkylene groups include methylene,
ethylene, propylene, butylene, and pentylene groups. Specific
examples of the alkenylene groups include vinylene, 1-propenylene,
2-propenylene, 1-butenylene, 2-butenylene, 1-pentenylene, and
2-pentenylene groups, with a vinylene group being more
preferred.
Examples of the C6-C10 aromatic hydrocarbon group for R.sup.13
include phenyl, benzyl, phenethyl, tolyl, xylyl, and naphthyl
groups. Preferred among these are phenyl, tolyl, and naphthyl
groups, with a phenyl group being more preferred.
Specific examples of the compound of formula (1) include vinyl
acetate, vinyl propionate, vinyl butyrate, vinyl hexanoate, vinyl
octanoate, vinyl decanoate, vinyl ethylhexanoate, vinyl crotonate,
vinyl benzoate, and vinyl cinnamate. Vinyl cinnamate is preferred
among these because it significantly improves the balance of fuel
economy, abrasion resistance, and wet grip performance while
ensuring good processability.
In the copolymer, the amount of the structural unit derived from a
compound of formula (1), based on 100% by mass of the structural
units of the copolymer, is preferably 5% by mass or more, more
preferably 10% by mass or more, still more preferably 20% by mass
or more. The amount is also preferably 95% by mass or less, more
preferably 70% by mass or less, still more preferably 50% by mass
or less, particularly preferably 40% by mass or less. When it is
less than 5% by mass, fuel economy may decrease. When it is more
than 95% by mass, abrasion resistance may decrease.
The copolymer may contain a structural unit other than the
structural unit derived from a conjugated diene monomer and the
structural unit derived from a compound of formula (1).
In the copolymer, the combined amount of the structural unit
derived from a conjugated diene monomer and the structural unit
derived from a compound of formula (1), based on 100% by mass of
the structural units of the copolymer, is preferably 60% by mass or
more, more preferably 80% by mass or more, still more preferably
90% by mass or more, and may be 100% by mass. When the combined
amount falls within the range indicated above, the effects of the
present invention can be better achieved.
The copolymer may contain a structural unit derived from a compound
represented by the formula (2) below. When the copolymer contains a
structural unit derived from a compound of formula (2), preferably
styrene, in addition to the structural unit derived from a
conjugated diene monomer and the structural unit derived from a
compound of formula (1), wet grip performance and abrasion
resistance (especially wet grip performance) can be more
significantly improved, and therefore the balance of fuel economy,
abrasion resistance, and wet grip performance can be more
significantly improved while ensuring good processability.
##STR00004##
In formula (2), R.sup.21 represents a hydrogen atom, a C1-C3
aliphatic hydrocarbon group, a C3-C8 alicyclic hydrocarbon group,
or a C6-C10 aromatic hydrocarbon group, and R.sup.22 represents a
hydrogen atom or a methyl group.
Examples of the C1-C3 aliphatic hydrocarbon group in the compound
of formula (2) include C1-C3 alkyl groups such as methyl, ethyl,
n-propyl, and isopropyl groups, with a methyl group being
preferred.
Examples of the C3-C8 alicyclic hydrocarbon group in the compound
of formula (2) include cyclopropyl, cyclobutyl, cyclopentyl,
cyclohexyl, cycloheptyl, cyclooctyl, cyclopropenyl, cyclobutenyl,
cyclopentenyl, cyclohexenyl, cycloheptenyl, and cyclooctenyl
groups.
Examples of the C6-C10 aromatic hydrocarbon group in the compound
of formula (2) include phenyl, benzyl, phenethyl, tolyl, xylyl, and
naphthyl groups. In view of high reactivity, phenyl, tolyl, and
naphthyl groups are preferred among these, with a phenyl group
being more preferred.
R.sup.21 is preferably a C6-C10 aromatic hydrocarbon group.
R.sup.22 is preferably a hydrogen atom.
Examples of the compound of formula (2) include styrene,
2-methylstyrene, 3-methylstyrene, 4-methylstyrene,
.alpha.-methylstyrene, 2,4-dimethylstyrene, vinylethylbenzene,
.alpha.-vinylnaphthalene, .beta.-vinylnaphthalene, and vinylxylene.
In view of high reactivity, styrene, .alpha.-methylstyrene,
.alpha.-vinylnaphthalene, and .beta.-vinylnaphthalene are preferred
among these, with styrene being more preferred.
In the copolymer, the amount of the structural unit derived from a
compound of formula (2), based on 100% by mass of the structural
units of the copolymer, is preferably 1% by mass or more, more
preferably 5% by mass or more, still more preferably 10% by mass or
more. The amount is also preferably 50% by mass or less, more
preferably 30% by mass or less, still more preferably 20% by mass
or less. When the amount falls within the range indicated above,
the effects of the present invention can be better achieved.
In the copolymer, the combined amount of the structural unit
derived from a compound of formula (1) and the structural unit
derived from a compound of formula (2), based on 100% by mass of
the structural units of the copolymer, is preferably 5% by mass or
more, more preferably 10% by mass or more, still more preferably
20% by mass or more. The combined amount is also preferably 95% by
mass or less, more preferably 70% by mass or less, still more
preferably 50% by mass or less, particularly preferably 40% by mass
or less. When the combined amount falls within the range indicated
above, the effects of the present invention can be better
achieved.
The amounts of the structural unit derived from a conjugated diene
monomer, the structural unit derived from a compound of formula
(1), and other structural units in the copolymer can be measured by
NMR (e.g. available from Bruker).
The copolymer may be produced by any copolymerization method, such
as solution polymerization, emulsion polymerization, gas phase
polymerization, or bulk polymerization. Emulsion polymerization is
preferred because this method produces a high yield of copolymers
with a high degree of monomer randomness.
In the case of emulsion polymerization, the copolymer can be
synthesized by known emulsion polymerization processes. For
example, the copolymer may be suitably produced by a method
including the steps of: emulsifying the monomers constituting the
copolymer, i.e. a diene monomer and a compound of formula (1), and
optionally a compound of formula (2) in water using an emulsifier;
and adding a radical initiator to the resulting emulsion to cause
radical polymerization.
The emulsion may be prepared by a known emulsification method using
an emulsifier. The emulsifier is not particularly limited, and may
be any known material, such as a fatty acid salt or a rosin acid
salt. Examples of the fatty acid salt or rosin acid salt include
potassium or sodium salts of capric acid, lauric acid, and myristic
acid.
The emulsion polymerization can be carried out by known methods
using radical polymerization initiators. Any radical polymerization
initiator may be used including known materials, e.g. redox
initiators such as paramenthane hydroperoxide, and persulfates such
as ammonium persulfate.
The temperature in the emulsion polymerization may be appropriately
adjusted according to the type of radical initiator used, and it
preferably ranges from -30.degree. C. to 50.degree. C., more
preferably from -10.degree. C. to 20.degree. C.
The emulsion polymerization can be terminated by adding a
polymerization terminator to the polymerization system. Any
polymerization terminator may be used including known materials,
e.g. N,N'-dimethyldithiocarbamate, diethylhydroxylamine, and
hydroquinone.
The copolymer in the present invention is preferably produced by
emulsion polymerization in the presence of a chain transfer agent.
The thus produced copolymer further improves processability, fuel
economy, and abrasion resistance.
A chain transfer agent refers to a radical polymerization
controlling agent that can act on the growing polymer chain end to
terminate the polymer growth while generating a new
polymerization-initiating radical. This agent enables control of
the molecular weight and molecular weight distribution of the
polymer (reduction of the molecular weight and narrowing of the
molecular weight distribution), control of the polymer chain end
structure, and other functions.
Examples of the chain transfer agent include compounds containing a
mercapto group, such as n-octyl mercaptan, n-nonyl mercaptan,
n-decyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and
n-hexadecyl mercaptan, with t-dodecyl mercaptan being preferred
because of easier control of the molecular weight.
The chain transfer agent may also suitably be a compound that
contains a functional group having an affinity for filler and a
mercapto group. When a compound that contains a mercapto group and
further a functional group having an affinity for filler is used as
the chain transfer agent, the functional group having an affinity
for filler will be introduced into the polymer chain end, with the
result that fuel economy, wet grip performance, and abrasion
resistance can be more significantly improved. Examples of the
functional group having an affinity for filler include amino,
amide, alkoxysilyl, isocyanate, imino, imidazole, urea, ester,
ether, carbonyl, carboxyl, hydroxyl, nitrile, and pyridyl groups.
Preferred among these are alkoxysilyl and ester groups, with
alkoxysilyl groups being more preferred. The term "filler" refers
to reinforcing filler such as carbon black or silica.
The compound containing an alkoxysilyl group may suitably be a
compound represented by the formula (3) below. In this case, fuel
economy, wet grip performance, and abrasion resistance can be more
significantly improved.
##STR00005##
In formula (3), R.sup.31 to R.sup.33 may be the same as or
different from one another and each represent a branched or
unbranched C1-C12 alkyl group, a branched or unbranched C1-C12
alkoxy group, or a group represented by
--O--(R.sup.35--O).sub.z--R.sup.36 where R.sup.35 groups, the
number of which is indicated by z, may be the same as or different
from one another and each represent a branched or unbranched
divalent C1-C30 hydrocarbon group, R.sup.36 represents a branched
or unbranched C1-C30 alkyl group, a branched or unbranched C2-C30
alkenyl group, a C6-C30 aryl group, or a C7-C30 aralkyl group, and
z represents an integer of 1 to 30, provided that at least one of
R.sup.31 to R.sup.33 is a branched or unbranched C1-C12 alkoxy
group; and R.sup.34 represents a branched or unbranched C1-C6
alkylene group.
R.sup.31 to R.sup.33 each represent a branched or unbranched C1-C12
alkyl group, a branched or unbranched C1-C12 alkoxy group, or a
group represented by --O--(R.sup.35--O).sub.z--R.sup.36, and at
least one of R.sup.31 to R.sup.33 is a branched or unbranched
C1-C12 alkoxy group.
In order to better achieve the effects of the present invention,
further at least one of R.sup.31 to R.sup.33 is preferably a group
represented by --O--(R.sup.35--O).sub.z--R.sup.36. More preferably,
the other two of R.sup.31 to R.sup.33 are groups represented by
--O--(R.sup.35--O).sub.z--R.sup.36.
Also preferably, all of R.sup.31 to R.sup.33 are branched or
unbranched alkoxy groups each having 1 to 12 carbon atoms,
preferably 1 to 5 carbon atoms, more preferably 1 to 3 carbon
atoms.
Examples of the branched or unbranched C1-C12, preferably C1-C5
alkyl group for R.sup.31 to R.sup.33 include methyl, ethyl,
n-propyl, isopropyl, n-butyl, iso-butyl, sec-butyl, tert-butyl,
pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, and nonyl groups.
Examples of the branched or unbranched C1-C12, preferably C1-C5,
more preferably C1-C3 alkoxy group for R.sup.31 to R.sup.33 include
methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, iso-butoxy,
sec-butoxy, tert-butoxy, pentyloxy, hexyloxy, heptyloxy,
2-ethylhexyloxy, octyloxy, and nonyloxy groups.
In the group: --O--(R.sup.35--O).sub.z--R.sup.36 for R.sup.31 to
R.sup.33, R.sup.35 represents a branched or unbranched divalent
hydrocarbon group having 1 to 30 carbon atoms, preferably 1 to 15
carbon atoms, more preferably 1 to 3 carbon atoms.
Examples of the hydrocarbon group include branched or unbranched
C1-C30 alkylene groups, branched or unbranched C2-C30 alkenylene
groups, branched or unbranched C2-C30 alkynylene groups, and C6-C30
arylene groups, with branched or unbranched C1-C30 alkylene groups
being preferred.
Examples of branched or unbranched C1-C30, preferably C1-C15, more
preferably C1-C3 alkylene groups for R.sup.35 include methylene,
ethylene, propylene, butylene, pentylene, hexylene, heptylene,
octylene, nonylene, decylene, undecylene, dodecylene, tridecylene,
tetradecylene, pentadecylene, hexadecylene, heptadecylene, and
octadecylene groups.
Examples of branched or unbranched C2-C30, preferably C2-C15, more
preferably C2-C3 alkenylene groups for R.sup.35 include vinylene,
1-propenylene, 2-propenylene, 1-butenylene, 2-butenylene,
1-pentenylene, 2-pentenylene, 1-hexenylene, 2-hexenylene, and
1-octenylene groups.
Examples of branched or unbranched C2-C30, preferably C2-C15, more
preferably C2-C3 alkynylene groups for R.sup.35 include ethynylene,
propynylene, butynylene, pentynylene, hexynylene, heptynylene,
octynylene, nonynylene, decynylene, undecynylene, and dodecynylene
groups.
Examples of C6-C30, preferably C6-C15 arylene groups for R.sup.35
include phenylene, tolylene, xylylene, and naphthylene groups.
The symbol z represents an integer of 1 to 30, preferably of 2 to
20, more preferably of 3 to 7, still more preferably of 5 or 6.
R.sup.36 represents a branched or unbranched C1-C30 alkyl group, a
branched or unbranched C2-C30 alkenyl group, a C6-C30 aryl group,
or a C7-C30 aralkyl group, preferably a branched or unbranched
C1-C30 alkyl group.
Examples of branched or unbranched C1-C30, preferably C3-C25, more
preferably C10-C15 alkyl groups for R.sup.36 include methyl, ethyl,
n-propyl, isopropyl, n-butyl, iso-butyl, sec-butyl, tert-butyl,
pentyl, hexyl, heptyl, 2-ethylhexyl, octyl, nonyl, decyl, undecyl,
dodecyl, tridecyl, tetradecyl, pentadecyl, and octadecyl
groups.
Examples of branched or unbranched C2-C30, preferably C3-C25, more
preferably C10-C15 alkenyl groups for R.sup.36 include vinyl,
1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 1-pentenyl,
2-pentenyl, 1-hexenyl, 2-hexenyl, 1-octenyl, decenyl, undecenyl,
dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, and octadecenyl
groups.
Examples of C6-C30, preferably C10-C20 aryl groups for R.sup.36
include phenyl, tolyl, xylyl, naphthyl, and biphenyl groups.
Examples of C7-C30, preferably C10-C20 aralkyl groups for R.sup.36
include benzyl and phenethyl groups.
Specific examples of the group represented by
--O--(R.sup.35--O).sub.z--R.sup.36 include --O--
(C.sub.2H.sub.4--O).sub.5--C.sub.11H.sub.23,
--O--(C.sub.2H.sub.4--O).sub.5--C.sub.12H.sub.25,
--O--(C.sub.2H.sub.4--O).sub.5--C.sub.13H.sub.27,
--O--(C.sub.2H.sub.4--O).sub.5--C.sub.14H.sub.29,
--O--(C.sub.2H.sub.4--O).sub.5--C.sub.15H.sub.31,
--O--(C.sub.2H.sub.4--O).sub.3--C.sub.13H.sub.27,
--O--(C.sub.2H.sub.4--O).sub.4C.sub.13H.sub.27,
--O--(C.sub.2H.sub.4--O).sub.6--C.sub.13H.sub.27, and
--O--(C.sub.2H.sub.4--O).sub.7--C.sub.13H.sub.27. Preferred among
these are --O--(C.sub.2H.sub.4--O).sub.5--C.sub.11H.sub.23,
--O--(C.sub.2H.sub.4--O).sub.5--C.sub.13H.sub.27,
--O--(C.sub.2H.sub.4--O).sub.5C.sub.15H.sub.31, and
--O--(C.sub.2H.sub.4--O).sub.6--C.sub.13H.sub.27.
Examples of the branched or unbranched C1-C6, preferably C1-C5
alkylene group for R.sup.34 include C1-C6 groups as described for
the branched or unbranched C1-C30 alkylene groups for R.sup.35.
Examples of the compound of formula (3) include
3-mercaptopropyltrimethoxysilane, 3-mercaptopropyl-triethoxysilane,
2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane,
and the compound (Si363 available from EVONIK-DEGUSSA) represented
by the formula below. In order to better achieve the effects of the
present invention, the compound of formula (3) may suitably be
3-mercaptopropyltriethoxysilane or the compound of the formula
below, more suitably the compound of the formula below. These
compounds may be used alone, or two or more of these may be used in
combination.
##STR00006##
The compound containing an ester group may suitably be a compound
represented by the formula (4) below. In this case, fuel economy,
wet grip performance, and abrasion resistance can be more
significantly improved. R.sup.41-A-R.sup.42--SH (4)
In formula (4), R.sup.41 represents a branched or unbranched C1-C12
alkyl group; R.sup.42 represents a branched or unbranched C1-C6
alkylene group; and A represents an ester group represented by
--COO-- or --OCO--.
Examples of the branched or unbranched C1-C12, preferably C5-C10
alkyl group for R.sup.41 include those described for the branched
or unbranched C1-C12 alkyl groups for R.sup.31 to R.sup.33.
Examples of the branched or unbranched C1-C6, preferably C1-C3
alkylene group for R.sup.42 include C1-C6 groups as described for
the branched or unbranched C1-C30 alkylene groups for R.sup.35.
Suitable examples of the compound of formula (4) include methyl
3-mercaptopropionate, ethyl 3-mercaptopropionate, propyl
3-mercaptopropionate, butyl 3-mercaptopropionate, pentyl
3-mercaptopropionate, hexyl 3-mercaptopropionate, heptyl
3-mercaptopropionate, octyl 3-mercaptopropionate, 2-ethylhexyl
3-mercaptopropionate, 2-ethylhexyl mercaptoethanoate,
2-mercaptoethyl methanoate, 2-mercaptoethyl ethanoate,
2-mercaptoethyl propionate, 2-mercaptoethyl butanoate,
2-mercaptoethyl pentanoate, 2-mercaptoethyl hexanoate,
2-mercaptoethyl heptanoate, 2-mercaptoethyl octanoate, and
2-mercaptomethyl octanoate, with 2-ethylhexyl 3-mercaptopropionate
or 2-mercaptoethyl octanoate being preferred. These compounds may
be used alone, or two or more of these may be used in
combination.
The copolymer preferably has a weight average molecular weight (Mw)
of 5,000 or more, more preferably 50,000 or more, still more
preferably 100,000 or more, particularly preferably 300,000 or
more, most preferably 450,000 or more. The weight average molecular
weight is also preferably 2,000,000 or less, more preferably
1,500,000 or less, still more preferably 1,000,000 or less,
particularly preferably 700,000 or less. When it is less than
5,000, fuel economy and abrasion resistance may deteriorate. When
it is more than 2,000,000, processability may deteriorate.
The copolymer preferably has a ratio of the Mw to the number
average molecular weight (Mn), that is, a molecular weight
distribution (Mw/Mn), of 2.1 or more, more preferably 2.5 or more,
still more preferably 3.0 or more, particularly preferably 3.8 or
more. The molecular weight distribution is also preferably 11 or
less, more preferably 8.0 or less, still more preferably 5.0 or
less. When it is less than 2.1, processability may deteriorate.
When it is more than 11, fuel economy may deteriorate.
The Mw and Mn values are determined by gel permeation
chromatography (GPC) calibrated with polystyrene standards.
The copolymer preferably has a glass transition temperature (Tg) of
-100.degree. C. to 100.degree. C., more preferably -70.degree. C.
to 0.degree. C. When the Tg falls within the range indicated above,
the effects of the present invention can be sufficiently
achieved.
The Tg values are measured with a differential scanning calorimeter
(Q200, available from TA Instruments, Japan) at a temperature
increase rate of 10.degree. C./min in accordance with JIS K
7121:1987.
The copolymer preferably has a Mooney viscosity, ML.sub.1+4, at
130.degree. C. of 30 to 100, more preferably 40 to 80. When the
ML.sub.1+4 falls within the range indicated above, the effects of
the present invention can be sufficiently achieved.
The Mooney viscosity (ML.sub.1+4, 130.degree. C.) values are
determined by measuring Mooney viscosity at 130.degree. C. in
accordance with JIS K 6300.
In the rubber composition of the present invention, the amount of
the copolymer based on 100% by mass of the rubber component is
preferably 1% by mass or more, more preferably 50% by mass or more,
still more preferably 70% by mass or more, particularly preferably
80% by mass or more, and may be 100% by mass. Less than 1% by mass
of the copolymer may be too little to achieve the effects of the
present invention.
Examples of other rubber materials that can be used in combination
with the copolymer in the rubber component in the present invention
include diene rubbers such as natural rubber (NR), polyisoprene
rubber (IR), polybutadiene rubber (BR), styrene-butadiene rubber
(SBR), styrene-isoprene rubber (SIR), styrene-isoprene-butadiene
rubber (SIBR), ethylene-propylene-diene rubber (EPDM), chloroprene
rubber (CR), acrylonitrile-butadiene rubber (NBR), and butyl rubber
(IIR). These diene rubbers may be used alone, or two or more of
these may be used in combination.
The rubber composition of the present invention contains carbon
black and/or silica as filler.
The carbon black may be one commonly used in tire production, and
examples include SAF, ISAF, HAF, FF, FEF, and GPF. These materials
may be used alone, or two or more of these may be used in
combination.
The carbon black preferably has a nitrogen adsorption specific
surface area (N.sub.2SA) of 80 m.sup.2/g or more, more preferably
100 m.sup.2/g or more. The N.sub.2SA is also preferably 200
m.sup.2/g or less, more preferably 150 m.sup.2/g or less. Carbon
black having a N.sub.2SA of less than 80 m.sup.2/g tends to provide
low reinforcing properties, failing to sufficiently improve
abrasion resistance. Carbon black having a N.sub.2SA of more than
200 m.sup.2/g tends to poorly disperse, thereby deteriorating fuel
economy.
The N.sub.2SA of carbon black can be measured in accordance with
JIS K 6217-2:2001.
The carbon black preferably has a dibutyl phthalate oil absorption
(DBP) of 50 mL/100 g or more, more preferably 100 mL/100 g or more.
The DBP is also preferably 200 mL/100 g or less, more preferably
150 mL/100 g or less. Carbon black having a DBP of less than 50
mL/100 g may provide insufficient reinforcing properties, resulting
in reduced abrasion resistance. Carbon black having a DBP of more
than 200 mL/100 g may have lower dispersibility, thereby
deteriorating fuel economy.
The DBP of carbon black can be measured in accordance with JIS K
6217-4:2001.
The amount of carbon black per 100 parts by mass of the rubber
component is preferably 1 part by mass or more, more preferably 3
parts by mass or more. The amount is also preferably 50 parts by
mass or less, more preferably 30 parts by mass or less, still more
preferably 20 parts by mass or less. When it is less than 1 part by
mass, abrasion resistance may deteriorate. When it is more than 50
parts by mass, fuel economy may deteriorate.
Non-limiting examples of the silica include dry silica (anhydrous
silicic acid) and wet silica (hydrous silicic acid). Wet silica is
preferred because it has a large number of silanol groups.
The silica preferably has a N.sub.2SA of 100 m.sup.2/g or more,
more preferably 150 m.sup.2/g or more. The N.sub.2SA is also
preferably 300 m.sup.2/g or less, more preferably 200 m.sup.2/g or
less. Silica having a N.sub.2SA of less than 100 m.sup.2/g tends to
have a low reinforcing effect, failing to sufficiently improve
abrasion resistance. Silica having a N.sub.2SA of more than 300
m.sup.2/g tends to poorly disperse, thereby deteriorating fuel
economy.
The N.sub.2SA of silica can be measured in accordance with ASTM
D3037-81.
The amount of silica per 100 parts by mass of the rubber component
is preferably 1 part by mass or more, more preferably 10 parts by
mass or more, still more preferably 30 parts by mass or more,
particularly preferably 50 parts by mass or more. The amount is
also preferably 150 parts by mass or less, more preferably 100
parts by mass or less. When it is less than 1 part by mass, fuel
economy and abrasion resistance tend to be insufficient. More than
150 parts by mass of silica tends to poorly disperse, thereby
deteriorating processability.
The rubber composition of the present invention preferably contains
a silane coupling agent together with silica.
The silane coupling agent may be any silane coupling agent
conventionally used in combination with silica in the rubber
industry. Examples include sulfide silane coupling agents such as
bis(3-triethoxysilylpropyl)tetrasulfide; mercapto silane coupling
agents such as 3-mercaptopropyl-trimethoxysilane; vinyl silane
coupling agents such as vinyltriethoxysilane; amino silane coupling
agents such as 3-aminopropyltriethoxysilane; glycidoxy silane
coupling agents such as .gamma.-glycidoxypropyltriethoxysilane;
nitro silane coupling agents such as
3-nitropropyl-trimethoxysilane; and chloro silane coupling agents
such as 3-chloropropyltrimethoxysilane. Preferred among these are
sulfide silane coupling agents, with
bis(3-triethoxysilylpropyl)tetrasulfide being more preferred.
In the case of the rubber composition containing a silane coupling
agent, the amount of the silane coupling agent per 100 parts by
mass of silica is preferably 1 part by mass or more, more
preferably 2 parts by mass or more. The amount is also preferably
20 parts by mass or less, more preferably 15 parts by mass or less.
An amount of less than 1 part by mass tends to fail to have
sufficient effects, e.g., in improving dispersibility. An amount of
more than 20 parts by mass tends to have an insufficient coupling
effect, resulting in reduced reinforcing properties.
The rubber composition of the present invention may optionally
incorporate compounding agents conventionally used in the rubber
industry, in addition to the components described above. Examples
of such agents include other reinforcing fillers, antioxidants,
oils, waxes, vulcanizing agents such as sulfur, and vulcanization
accelerators.
The rubber composition of the present invention may be used in
treads (cap treads, base treads), sidewalls, and other components
of tires and is suitable especially for treads, particularly cap
treads.
The pneumatic tire of the present invention can be formed from the
above-described rubber composition by usual methods.
Specifically, the rubber composition incorporating the components
described above, before vulcanization, is extruded and processed
into the shape of a tire component, e.g. a tread and assembled with
other tire components on a tire building machine in a usual manner
to build an unvulcanized tire. The unvulcanized tire is heated and
pressurized in a vulcanizer to obtain a tire.
The pneumatic tire of the present invention is suitable for
passenger vehicles, large passenger vehicles, large SUVs,
heavy-duty vehicles such as trucks and buses, and light trucks, and
may be used as a winter tire or studless winter tire for these
vehicles.
EXAMPLES
The present invention is specifically described with reference to
examples but is not limited only thereto.
The chemicals used in production examples are listed below.
Ion-exchanged water: in-house product
Potassium rosinate soap: available from Harima Chemicals Group,
Inc.
Fatty acid sodium soap: available from Wako Pure Chemical
Industries, Ltd.
Potassium chloride: available from Wako Pure Chemical Industries,
Ltd.
Sodium naphthalenesulfonate-formaldehyde condensate: available from
Kao Corporation
1,3-Butadiene: 1,3-butadiene available from Takachiho Trading Co.,
Ltd.
Styrene: styrene available from Wako Pure Chemical Industries, Ltd.
(a compound of formula (2))
t-Dodecyl mercaptan: tert-dodecyl mercaptan available from Wako
Pure Chemical Industries, Ltd. (chain transfer agent)
Si363:
3-[ethoxybis(3,6,9,12,15-pentaoxaoctacosan-1-yloxy)silyl]-1-propan-
ethiol available from Degussa (chain transfer agent, the compound
represented by the formula below, a compound of formula (3))
##STR00007##
3-Mercaptopropyltriethoxysilane: product available from Tokyo
Chemical Industry Co., Ltd. (chain transfer agent, a compound of
formula (3))
2-Ethylhexyl 3-mercaptopropionate: product available from Tokyo
Chemical Industry Co., Ltd. (chain transfer agent, a compound of
formula (4))
2-Mercaptoethyl octanoate: product available from Tokyo Chemical
Industry Co., Ltd. (chain transfer agent, a compound of formula
(4))
Sodium hydrosulfide: available from Wako Pure Chemical Industries,
Ltd.
FeSO.sub.4: ferric sulfate available from Wako Pure Chemical
Industries, Ltd.
EDTA: sodium ethylenediaminetetraacetate available from Wako Pure
Chemical Industries, Ltd.
Rongalite: sodium formaldehyde sulfoxylate available from Wako Pure
Chemical Industries, Ltd.
Polymerization initiator: PERMENTA H (paramenthane hydroperoxide)
available from NOF Corporation
N,N-Diethylhydroxylamine: available from Wako Pure Chemical
Industries, Ltd.
2,6-Di-t-butyl-p-cresol: Sumilizer BHT available from Sumitomo
Chemical Co., Ltd.
Vinyl cinnamate: product available from Tokyo Chemical Industry
Co., Ltd. (a compound of formula (1))
(Preparation of Emulsifier)
An emulsifier was prepared by adding 9,356 g of ion-exchanged
water, 1,152 g of potassium rosinate soap, 331 g of fatty acid
sodium soap, 51 g of potassium chloride, and 30 g of sodium
naphthalenesulfonate-formaldehyde condensate, followed by stirring
at 70.degree. C. for 2 hours.
Production Example 1
A 50 L (interior volume) stainless steel polymerization reactor was
cleaned, dried, and purged with dry nitrogen. Then, the reactor was
charged with 3,500 g of 1,3-butadiene, 1,500 g of styrene, 5.74 g
of t-dodecyl mercaptan, 9,688 g of the emulsifier, 6.3 mL of sodium
hydrosulfide (1.8 M), 6.3 mL each of the activators
(FeSO.sub.4/EDTA/Rongalite), and 6.3 mL of the polymerization
initiator (2.3 M), followed by polymerization at 10.degree. C. for
3 hours with stirring. After the completion of the polymerization,
2.9 g of N,N-diethylhydroxylamine was added to the reaction mixture
and they were reacted for 30 minutes. The contents were taken out
from the polymerization reactor and combined with 10 g of
2,6-di-t-butyl-p-cresol. After most of the water was evaporated
off, the residue was dried under reduced pressure at 55.degree. C.
for 12 hours to obtain copolymer 1.
Production Example 2
Copolymer 2 was prepared as in Production Example 1, except that
1,500 g of vinyl cinnamate was used instead of 1,500 g of
styrene.
Production Example 3
Copolymer 3 was prepared as in Production Example 1, except that
1,500 g of vinyl cinnamate was used instead of 1,500 g of styrene,
and 6.11 g of Si363 was used instead of 5.74 g of t-dodecyl
mercaptan.
Production Example 4
Copolymer 4 was prepared as in Production Example 1, except that
1,500 g of vinyl cinnamate was used instead of 1,500 g of styrene,
and 1.48 g of 3-mercaptopropyl-triethoxysilane was used instead of
5.74 g of t-dodecyl mercaptan.
Production Example 5
Copolymer 5 was prepared as in Production Example 1, except that
1,500 g of vinyl cinnamate was used instead of 1,500 g of styrene,
and 1.35 g of 2-ethylhexyl 3-mercaptopropionate was used instead of
5.74 g of t-dodecyl mercaptan.
Production Example 6
Copolymer 6 was prepared as in Production Example 1, except that
1,500 g of vinyl cinnamate was used instead of 1,500 g of styrene,
and 1.26 g of 2-mercaptoethyl octanoate was used instead of 5.74 g
of t-dodecyl mercaptan.
Table 1 shows the amount of butadiene (conjugated diene monomer),
amount of vinyl cinnamate (a compound of formula (1)), amount of
styrene, Mw, and Mw/Mn of copolymers 1 to 6 prepared in Production
Examples 1 to 6. These values were determined as collectively
described below.
(Amounts of Monomer Units)
A .sup.1H-NMR spectrum was measured using a JNM-A 400 NMR
spectrometer (available from JEOL) at 25.degree. C. This spectrum
was used to calculate the ratio of the phenyl protons of the
styrene unit at 6.5 to 7.2 ppm, the vinyl protons of the butadiene
unit at 4.9 to 5.4 ppm, and the protons of the vinyl-derived moiety
of the compound unit of formula (1) at 1.5 to 2.5 ppm. Then, the
amounts of the monomer units were determined from the ratio.
(Determination of Weight Average Molecular Weight (Mw) and Number
Average Molecular Weight (Mn))
The weight average molecular weight (Mw) and number average
molecular weight (Mn) of the copolymers were determined by gel
permeation chromatography (GPC) (GPC-8000 series available from
Tosoh Corporation, detector: differential refractometer, column:
TSKGEL SUPERMULTIPORE HZ-M available from Tosoh Corporation)
calibrated with polystyrene standards.
TABLE-US-00001 TABLE 1 Production Production Production Production
Production Production Example 1 Example 2 Example 3 Example 4
Example 5 Example 6 (Copolymer 1) (Copolymer 2) (Copolymer 3)
(Copolymer 4) (Copolymer 5) (Copolymer 6) Amount of butadiene
(conjugated 76 76 76 76 76 76 diene monomer) (% by mass) Amount of
vinyl cinnamate -- 24 24 24 24 24 (formula (1)) (% by mass) Amount
of styrene (% by mass) 24 -- -- -- -- -- Weight average molecular
weight 510,000 500,000 500,000 500,000 500,000 490,000 (Mw)
Molecular weight distribution 3.6 4.0 4.0 4.0 4.0 4.0 (Mw/Mn)
The chemicals used in examples and comparative example were listed
below.
Rubber component: Copolymer 1 to 6 prepared in Production Example 1
to 6
Carbon black: SHOBLACK N220 (N.sub.2SA: 111 m.sup.2/g, DBP: 115
mL/100 g) available from Cabot Japan K.K.
Silica: ULTRASIL VN3 (N.sub.2SA: 175 m.sup.2/g) available from
Degussa
Silane coupling agent: Si69
(bis(3-triethoxysilylpropyl)tetrasulfide) available from
Degussa
Zinc oxide: Zinc oxide #1 available from Mitsui Mining and Smelting
Co., Ltd.
Stearic acid: Stearic acid available from NOF Corporation
Antioxidant: NOCRAC 6C
(N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine) available from
Ouchi Shinko Chemical Industrial Co., Ltd.
Wax: Sunnoc Wax available from Ouchi Shinko Chemical Industrial
Co., Ltd.
Vulcanization accelerator 1: Nocceler CZ
(N-cyclohexyl-2-benzothiazolylsulfenamide) available from Ouchi
Shinko Chemical Industrial Co., Ltd.
Vulcanization accelerator 2: Nocceler D (N,N'-diphenylguanidine)
available from Ouchi Shinko Chemical Industrial Co., Ltd.
Sulfur: Sulfur powder available from Tsurumi Chemical Industry Co.,
Ltd.
EXAMPLES AND COMPARATIVE EXAMPLE
According to each of the formulations shown in Table 2, the
chemicals other than the sulfur and vulcanization accelerators were
kneaded using a Banbury mixer at 150.degree. C. for 5 minutes. To
the kneaded mixture were added the sulfur and vulcanization
accelerators, and they were kneaded using an open roll mill at
170.degree. C. for 12 minutes to obtain an unvulcanized rubber
composition.
The unvulcanized rubber composition was press-vulcanized at
170.degree. C. for 20 minutes to obtain a vulcanized rubber
composition.
The unvulcanized rubber compositions and vulcanized rubber
compositions prepared as above were evaluated as follows. Table 2
shows the results.
(Processability)
Each unvulcanized rubber composition was measured for Mooney
viscosity at 100.degree. C. in accordance with JIS K 6300. A lower
value indicates better processability.
(Wet Grip Performance)
The viscoelastic parameter of a specimen prepared from each
vulcanized rubber composition was determined using a
viscoelastometer (ARES, available from Rheometric Scientific) in a
torsional mode. The tan .delta. was measured at 0.degree. C., a
frequency of 10 Hz, and a strain of 1%. A higher tan .delta.
indicates better wet grip performance.
(Fuel Economy)
The tan .delta. of each vulcanized rubber composition was measured
using a viscoelasticity spectrometer VES (Iwamoto Seisakusho Co.,
Ltd.) at a temperature of 60.degree. C., an initial strain of 10%,
and a dynamic strain of 2%. A lower tan .delta. indicates better
fuel economy.
(Abrasion Resistance)
The abrasion loss of each vulcanized rubber composition was
measured with a Lambourn abrasion tester at room temperature, an
applied load of 1.0 kgf, and a slip ratio of 30% and expressed as
an index using the equation below. A higher index indicates better
abrasion resistance. (Abrasion resistance index)=(Abrasion loss of
Comparative Example 1)/(Abrasion loss of each formulation
example).times.100
TABLE-US-00002 TABLE 2 Comparative Example 1 Example 1 Example 2
Example 3 Example 4 Example 5 Formulation Rubber component
Copolymer 1 Copolymer 2 Copolymer 3 Copolymer 4 Copolymer 5
Copolymer 6 (parts by mass) 100 100 100 100 100 100 Carbon black 5
5 5 5 5 5 Silica 75 75 75 75 75 75 Silane coupling agent 6 6 6 6 6
6 Zinc oxide 2 2 2 2 2 2 Stearic acid 2 2 2 2 2 2 Antioxidant 2 2 2
2 2 2 Wax 2 2 2 2 2 2 Vulcanization accelerator 1 1.5 1.5 1.5 1.5
1.5 1.5 Vulcanization accelerator 2 2 2 2 2 2 2 Sulfur 1.5 1.5 1.5
1.5 1.5 1.5 Evaluation Processability 61 54 61 61 59 59 Wet grip
performance 0.454 0.522 0.54 0.539 0.532 0.529 Fuel economy 0.228
0.216 0.193 0.196 0.209 0.208 Abrasion resistance index 100 115 125
125 127 128
Table 2 demonstrates that a balanced improvement in fuel economy,
abrasion resistance, and wet grip performance was achieved while
ensuring good processability in the examples in which copolymers 2
to 6 containing a structural unit derived from a conjugated diene
monomer and a structural unit derived from a compound of formula
(1) were incorporated together with carbon black and/or silica.
* * * * *