U.S. patent application number 16/988953 was filed with the patent office on 2020-11-26 for tire containing silicate microflakes having enhanced traction characteristics.
The applicant listed for this patent is The Goodyear Tire & Rubber Company. Invention is credited to Paul Harry Sandstrom, John Joseph Andre Verthe, Ping Zhang.
Application Number | 20200368984 16/988953 |
Document ID | / |
Family ID | 1000005005046 |
Filed Date | 2020-11-26 |
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United States Patent
Application |
20200368984 |
Kind Code |
A1 |
Sandstrom; Paul Harry ; et
al. |
November 26, 2020 |
TIRE CONTAINING SILICATE MICROFLAKES HAVING ENHANCED TRACTION
CHARACTERISTICS
Abstract
This invention discloses a tire having enhanced wet traction and
ice traction characteristics. These tires are comprised of a
generally toroidal-shaped carcass with an outer circumferential
tread, two spaced beads, at least one ply extending from bead to
bead and sidewalls extending radially from and connecting said
tread to said beads, wherein said tread is adapted to be
ground-contacting, wherein the tread includes at least one
circumferential groove which separates circumferential ribs, each
circumferential groove having two sides and a base therebetween,
and wherein the sides of each circumferential groove are comprised
of a rubbery composition that includes silicate microflakes which
are substantially aligned in an orientation which is parallel with
the sides of the grooves.
Inventors: |
Sandstrom; Paul Harry;
(Cuyahoga Falls, OH) ; Verthe; John Joseph Andre;
(Kent, OH) ; Zhang; Ping; (Westford, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Goodyear Tire & Rubber Company |
Akron |
OH |
US |
|
|
Family ID: |
1000005005046 |
Appl. No.: |
16/988953 |
Filed: |
August 10, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14492660 |
Sep 22, 2014 |
10744733 |
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16988953 |
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13218507 |
Aug 26, 2011 |
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14492660 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60C 2011/142 20130101;
B29K 2995/0097 20130101; B60C 11/1346 20130101; B29D 30/66
20130101; B29D 2030/667 20130101; B29K 2023/22 20130101; B60C
1/0016 20130101; B29K 2509/08 20130101; B29D 30/02 20130101; B29D
2030/665 20130101 |
International
Class: |
B29D 30/66 20060101
B29D030/66; B60C 11/13 20060101 B60C011/13; B60C 1/00 20060101
B60C001/00; B29D 30/02 20060101 B29D030/02 |
Claims
1. A tire which is comprised of a generally toroidal-shaped carcass
with an outer circumferential tread which is adapted to be ground
contacting, two spaced beads, at least one ply extending from bead
to bead and sidewalls extending radially from and connecting said
tread to said beads, wherein said tread is adapted to be
ground-contacting, wherein the tread includes at least one
circumferential groove which separates circumferential ribs, each
circumferential groove having two sides and a base which is
situated between the circumferential grooves, and wherein the sides
of each circumferential groove are comprised of a rubbery
composition that includes glass microflakes which are substantially
aligned in an orientation which is parallel with the sides of the
grooves, wherein the glass microflakes have a thickness which is
within the range of 2 microns to 40 microns, and wherein the glass
microflakes have a diameter which is within the range of 10 microns
to 40 microns, wherein the ground contacting surface of the tread
is substantially free of the glass microflakes, and wherein the
sides of each circumferential groove has a coefficient of friction
with water which is lower than the coefficient of friction of the
tread with water.
2. The tire as specified in claim 1 wherein the tire is a pneumatic
tire.
3. The tire as specified in claim 1 wherein the tire is a
non-pneumatic tire.
4. The tire as specified in claim 1 further including a carcass ply
radially inward of the tread.
5. The tire as specified in claim 1 wherein the glass microflakes
are present in the rubbery composition at a level which is within
the range of 1 to 40 parts by weight per 100 parts by weight of
rubber.
6. The tire as specified in claim 1 wherein the glass microflakes
are present in the rubbery composition at a level which is within
the range of 3 to 25 parts by weight per 100 parts by weight of
rubber.
7. The tire as specified in claim 1 wherein the microflakes have a
thickness which is within the range of 4 microns to 40 microns.
8. The tire as specified in claim 1 wherein the microflakes have a
thickness which is within the range of 6 microns to 40 microns.
9. The tire as specified in claim 1 wherein the microflakes have a
thickness which is within the range of 10 microns to 30
microns.
10. The tire as specified in claim 1 wherein the rubbery
composition is comprised of a brominated butyl rubber.
11. The tire as specified in claim 10 wherein the rubbery
composition is further comprised of a silica reinforcing
filler.
12. The tire as specified in claim 1 wherein the circumferential
ribs include a base portion which is free of glass microflakes.
13. The tire as specified in claim 1 wherein the glass microflakes
have disposed on at least part of their surface a composition
selected from the group consisting of an aliphatic fatty acid, a
synthetic microcrystalline wax, a Bunte salt, and a
polysulfide.
14. The tire as specified in claim 13 wherein the composition
selected from the group consisting of an aliphatic fatty acid, a
synthetic microcrystalline wax, a Bunte salt, and a polysulfide is
a synthetic microcrystalline wax.
15. The tire as specified in claim 14 wherein the microcrystalline
wax is a polyethylene wax.
16. The tire as specified in claim 7 wherein the glass microflakes
have a diameter which is within the range of 10 microns to 35
microns.
17. The tire as specified in claim 8 wherein the glass microflakes
have a diameter which is within the range of 10 microns to 30
microns.
18. The tire as specified in claim 7 wherein the glass microflakes
have a diameter which is within the range of 10 microns to 25
microns.
19. The tire as specified in claim 1 wherein the outside surface of
the sidewalls in the shoulder areas of the tire are covered with
the rubbery composition that includes the glass microflakes.
20. A tire which is comprised of a generally toroidal-shaped
carcass with an outer circumferential tread which is adapted to be
ground contacting, two spaced beads, at least one ply extending
from bead to bead and sidewalls extending radially from and
connecting said tread to said beads, wherein said tread is adapted
to be ground-contacting, wherein the tread includes at least one
circumferential groove which separates circumferential ribs, each
circumferential groove having two sides and a base which is
situated between the circumferential grooves, and wherein the sides
of each circumferential groove are comprised of a rubbery
composition that includes glass microflakes which are substantially
aligned in an orientation which is parallel with the sides of the
grooves, wherein the glass microflakes have a thickness which is
within the range of 2 microns to 40 microns, and wherein the glass
microflakes have a diameter which is within the range of 10 microns
to 40 microns, wherein the outside surface of the sidewalls in the
shoulder areas of the tire are covered with the rubbery composition
that includes the glass microflakes, and wherein the sides of each
circumferential groove has a coefficient of friction with water
which is lower than the coefficient of friction of the tread with
water.
Description
[0001] This is a divisional of U.S. patent application Ser. No.
14/492,660, filed on Sep. 22, 2014 (presently pending), which is a
divisional of U.S. patent application Ser. No. 13/218,507, filed on
Aug. 26, 2011 (now abandoned). The teachings of U.S. patent
application Ser. No. 14/492,660 and U.S. patent application Ser.
No. 13/218,507 are incorporated herein by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] A pneumatic tire typically includes a pair of axially
separated inextensible beads. A circumferentially disposed bead
filler apex extends radially outward from each respective bead. At
least one carcass ply extends between the two beads. The carcass
ply has axially opposite end portions, each of which is turned up
around a respective bead and secured thereto. Tread rubber and
sidewall rubber are located axially and radially outward,
respectively, of the carcass ply.
[0003] Achieving satisfactory performance in wet and icy conditions
requires special characteristics from a tire. Several different
features are used to achieve these characteristics. One such
feature is the tread combination of grooves and ribs which remove
water from the contact surface of the tire rubber and the road
surface so that sufficient performance can be achieved in wet
conditions. As a means of improving the flow of water through the
grooves of a tire, United States Patent Application Publication
Number 2007/0062623 A1 (now issued as U.S. Pat. No. 7,987,881 B2)
teaches a rubber tread for tires, comprising: a plurality of
elements in relief comprising lateral faces and one contact face
intended to be in contact along a surface with the roadway during
travel of a tire provided with said tread, the limit of the surface
of contact of the contact face with the ground forming at least one
ridge, a plurality of cutouts in the form of grooves and/or
incisions, said cutouts being defined by facing lateral faces, each
tread pattern element being formed with at least one first rubber
mix (referred to as "base mix"), wherein, viewed in section in a
plane containing the thickness of this tread, at least one face
defining at least one cutout is covered at least in part with a
second rubber mix, referred to as "covering mix", this part having
covering mix extending when new over a height Hr at least equal to
30% of the height of the face, wherein at least one base mix opens
on to the contact face when new or at the latest after wear at most
equal to 10% of the height Hr, said covering mix comprising a butyl
rubber, and wherein the covering mix comprises a plasticizer of the
unsaturated C.sub.12-C.sub.22 fatty acid ester type. Although wet
performance was improved with this type of tire tread, there was no
significant improvement in icy conditions.
[0004] Performance in icy conditions can be achieved by several
different means. One way to improve performance in these conditions
is to use a softer tread compound which increases the coefficient
of friction between the tire and the road. This typically has the
detrimental effects of increasing both the rolling resistance and
wear of the tread. To reduce the rolling resistance and wear of the
tread without compromising on the friction coefficient of the
tread, United States Patent Application Publication 2010/0154948
discloses a tire having an axis of rotation, wherein the tire
comprises: two sidewalls extending radially outward; and a tread
disposed radially outward of the two sidewalls and interconnecting
the two sidewalls, the tread comprising a main portion comprising a
first compound and a reinforcing structure comprising a second
compound having reinforcing short fibers oriented between
-20.degree. to +20.degree. to a circumferential direction of the
tread, the main portion of the tread comprising at least one
circumferential groove separating circumferential ribs, each
circumferential groove having two sides and a base which is
situated between the circumferential grooves, the reinforcing
structure comprising a layer of the second compound secured to the
sides of each circumferential groove.
[0005] Another way to improve traction in icy conditions is to use
studs. Using studs, however, causes damage to the road surface. To
attain a portion of the benefits of a studded tire without causing
damage to the road surface, United States Patent Application
Publication 2008/0041511 A1 discloses a vehicle tire, comprising; a
filler including glass flake. The glass flake, however, is not
oriented in any particular direction which provides only a portion
of the possible traction advantage while increasing the hardness of
the rubber compound.
[0006] U.S. Pat. No. 7,122,090 discloses a process for preparing a
studless tire having a tread comprising a rubber sheet having a
thickness of at most 20 mm, which comprises: extruding a rubber
composition containing 2 to 50 parts by weight of short fiber or
plate-like material having a Moh's hardness of 3 to 7 based on 100
parts by weight of diene rubber in a tube shape, thereby orienting
said short fiber or plate-like material in the circumferential
direction of said tube shaped rubber composition; cutting said tube
shaped rubber composition at one point in a sidewall thereof in the
extrusion direction to obtain a rubber sheet having a complex
elastic modulus Ea in the extrusion direction and complex elastic
modulus Eb in the 90.degree. direction from the extrusion direction
measured at 25.degree. C. which fulfill the following equation:
1.1.ltoreq.Eb/Ea; cutting said rubber sheet parallel to the
extrusion direction to obtain pieces; rotating each piece
90.degree. and laminating the rotated pieces together to form a
tread having a thickness of at most 20 mm; and forming a studless
tire having said tread. This tire tread has the advantage of
increased traction due to the short fibers or plate-like material
scratching the road surface, but requires a significant effort to
orient these elements. Therefore, there has been a long-felt need
for a tire tread which provides improved water channeling ability
and increased coefficient of friction with the road surface without
increased wear of the tire tread without a substantial increase in
manufacturing effort.
SUMMARY OF THE INVENTION
[0007] The present invention discloses a tire which is comprised of
a generally toroidal-shaped carcass with an outer circumferential
tread, two spaced beads, at least one ply extending from bead to
bead and sidewalls extending radially from and connecting said
tread to said beads, wherein said tread is adapted to be
ground-contacting, wherein the tread includes at least one
circumferential groove which separates circumferential ribs, each
circumferential groove having two sides and a base which is
situated between the circumferential grooves, and wherein the sides
of each circumferential groove are comprised of a rubbery
composition that includes silicate microflakes which are
substantially aligned in an orientation which is parallel with the
sides of the grooves.
[0008] In another embodiment of the present invention the tire is a
pneumatic tire. In yet another embodiment of the present invention
the tire is a non-pneumatic tire.
[0009] In still another embodiment of the present invention the
tire includes a carcass ply radially inward of the tread.
[0010] In one specific embodiment of the present invention the
microflakes have a thickness between about 0.02 microns and 40
microns and a diameter between about 2 microns to 250 microns. In
many cases the microflakes have a thickness which is within the
range of about 0.2 microns to 30 microns and a diameter which is
within the range of about 6 microns to 100 microns. It is typically
preferred for the microflakes have a thickness which is within the
range of about 0.4 microns to about 20 microns and a diameter which
is within the range of about 10 microns to 60 microns. The
microflakes are typically comprised of a member selected from the
group consisting of glass, mica, and clay. For instance, the
microflakes can be glass microflakes.
[0011] In one specific embodiment of the present invention the
rubbery composition is comprised of a brominated butyl rubber. The
rubbery composition can contain a silica reinforcing filler.
[0012] In still another embodiment of the present invention the
circumferential ribs include a base portion which is free of
silicate microflakes.
[0013] The present invention further discloses a process for
manufacturing a tire comprising: positioning a cover layer onto an
uncured tire having a generally toroidal-shaped carcass with an
outer circumferential tread portion, two spaced beads, at least one
ply extending from bead to bead and sidewalls extending radially
from and connecting said tread portion to said beads, wherein the
cover layer is comprised of a rubber compound including at least
one rubbery polymer and silicate microflakes, wherein the silicate
microflakes are embedded within the cover layer and positioned in
such a manner that they are aligned in the cover layer in a manner
whereby they are substantially parallel with the circumferential
surface of the tread portion of the uncured tire; placing the tire
into a curing mold to form a desired tire tread having at least one
circumferential groove which separates circumferential ribs, each
circumferential groove having two sides and a base therebetween,
wherein the silicate microflakes positioned on the sides of the
grooves are substantially aligned in an orientation which is
parallel with the sides of the grooves; maintaining the uncured
tired in the mold at an elevated temperature for a period of time
that is sufficient to cure the tire; and removing the tire from the
curing mold.
[0014] In yet another embodiment of the present invention the cover
layer is an extruded sheet of rubber.
[0015] Another embodiment of the present invention comprises
mechanically removing the cover layer from the circumferentially
outer most portion of the tread.
[0016] In still another embodiment of the present invention the
tread includes circumferential ribs, wherein the tread is adapted
to be ground-contacting, and wherein removal of the outer cover
results in the base rubber becoming the ground contacting area of
the ribs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic cross-sectional view of an example
tire for use with the tread region of the present invention.
[0018] FIG. 2 is a schematic detail cross-sectional view of the
tread region for use with the example tire of FIG. 1.
[0019] FIG. 2A is a schematic detail cross-sectional view of one
groove of the tread region for use with the example tire of FIG.
1.
[0020] FIG. 3 is a schematic detail cross-sectional view of the
tread region for use with the example tire of FIG. 1 with the
outermost portion of the cover layer removed.
[0021] FIG. 3A is a schematic detail cross-sectional view of one
groove of the tread region for use with the example tire of FIG. 1
with the outermost portion of the cover layer removed.
[0022] FIG. 4 is a schematic diagram depicting the process for
preparing the cover layer of rubber of the present invention.
[0023] FIG. 5 is a schematic cross sectional view of an apparatus
having an extruder and an extrusion head used in the process for
preparing the cover layer of rubber of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0024] FIG. 1 shows an example tire 10 for use with a cover layer
in accordance with the present invention. The example tire 10 has a
tread 12, an inner liner 23, a belt structure 16 comprising belts
18, 20, a carcass 22 with a carcass ply 14, two sidewalls 15,17,
and two bead regions 24a, 24b comprising bead filler apexes 26a,
26b and beads 28a, 28b. The example tire 10 is suitable, for
example, for mounting on a rim of a passenger vehicle. The carcass
ply 14 includes a pair of axially opposite end portions 30a, 30b,
each of which is secured to a respective one of the beads 28a, 28b.
Each axial end portion 30a or 30b of the carcass ply 14 is turned
up and around the respective bead 28a, 28b to a position sufficient
to anchor each axial end portion 30a, 30b.
[0025] The carcass ply 14 may be a rubberized ply having a
plurality of substantially parallel carcass reinforcing members
made of such material as polyester, rayon, or similar suitable
organic polymeric compounds. The turned up portions of the carcass
ply 14 may engage the axial outer surfaces of two flippers 32a, 32b
and axial inner surfaces of two chippers 34a, 34b.
[0026] In accordance with the present invention, as shown in FIG.
1, the example tread 12 has four circumferential grooves 41, each
having a lining comprising a U-shaped cover section 43. The
combination of the cover sections comprise the cover layer. The
main portion of the tread 12 may be formed of a first tread
compound, which may be any suitable tread compound or compounds.
Each cover section 43 occupies the inner surface of a
circumferential groove 41 and is formed of a second compound. The
second compound includes microflakes that are oriented in such a
manner as to be aligned with the cover section 43.
[0027] Each circumferential groove 41 is defined by a bottom or
base laterally separating a pair of radially extending walls
(U-shaped). As seen in FIG. 1, the cover section 43 completely
lines each circumferential groove 41, in lateral, radial, and
circumferential (not shown) directions. Each covering section 43
includes two radial portions 45, which form opposing walls of the
cover section 43 adjacent the radially extending walls of the
circumferential grooves 41. Each cover section 43 further has a
base portion 47 interconnecting the two radial portions 45 along
the base of the circumferential grooves 41. The microflakes in the
radial portions 45 are aligned to be parallel to a circumferential
direction of the tread 12 and the tire 10.
[0028] In accordance with another aspect of the present invention,
as shown in FIGS. 2 and 2A, the tire 10 may have a cover layer 142
which completely covers the outermost layer of the tread. The cover
layer 142 lines the circumferential grooves 141 and also covers the
base portion of the tread 12. The base portion of the tread 12 may
be formed of a first tread compound, which may be any suitable
tread compound, as described above with respect to FIG. 1. The
cover layer 142 is formed of a second compound. The second compound
includes silicate microflakes which are oriented in such a manner
that they are parallel to the cover layer. In the radial portions
143 and base portions 147 the microflakes will be aligned to a
circumferential direction of the tread 12 and the tire 10. Example
cover layer 142 may have a uniform thickness between 0.2 mm and 5.0
mm. Preferably cover layer 142 may have a uniform thickness between
0.5 mm and 1.5 mm.
[0029] The cover layer rubber formulation of this invention can be
used as the outermost layer of tire treads in conjunction with
ordinary tire manufacturing techniques. Tires are built utilizing
standard procedures with a sheet of the cover layer rubber
formulation of this invention simply replacing the outermost layer
of the base tread compound. After the tire has been built with the
cover layer rubber formulation of this invention, it can be
vulcanized using a normal tire cure cycle. Tires made in accordance
with this invention can be cured over a wide temperature range.
However, it is generally preferred for the tires of this invention
to be cured at a temperature ranging from about 132.degree. C.
(270.degree. F.) to about 166.degree. C. (330.degree. F.). It is
more typical for the tires of this invention to be cureutermost
layer of rubber around the tread rubber d at a temperature ranging
from about 143.degree. C. (290.degree. F.) to about 154.degree. C.
(310.degree. F.). It is generally preferred for the cure cycle used
to vulcanize the tires of this invention to have a duration of
about 10 to about 14 minutes with a cure cycle of about 12 minutes
being most preferred.
[0030] In accordance with another aspect of the present invention,
the cover layer 143 may be mechanically removed from the outermost
surface of the base portion of the tread 12 leaving the second
compound lining the radial portions 143 and base portions 147 of
the grooves. The removal of the cover layer 143 from the outermost
surface of the base portion of the tread 12 can be accomplished for
example by grinding the cover layer 143 from the ground contacting
surface of the tread 12. Alternatively the cover layer 142 may be
left in place to be worn away during use of the tire 10.
[0031] Because the second compound lining the radial portions 143
and base portions 147 of the grooves 141 has a lower coefficient of
friction with water, the water will be carried through the grooves
141 at a faster rate. In wet conditions, faster removal of the
water from the grooves 141 at increases the direct contact between
the tire and the road surface because the water which is on the
road surface can be more easily moved away from the contact
surface.
[0032] When the cover layer is removed from the outermost layer of
the tread, silicate microflakes are left at the road contacting
surface of the radial portions 143 of the grooves. These
microflakes are aligned with the radial portions 143 and therefore
will have contact the road surface in a blade like manner. This
interaction between the road surface and the silicate microflakes,
leads to a higher coefficient of friction than could be attained
through use of rubber alone. This is particularly useful in icy
conditions.
[0033] The specific composition and physical properties of the
first compound of the tread 12 and the second compound of the cover
sections 43 or 243, and the relationships therebetween, will now be
discussed. Modulus of elasticity E may measure, among other
characteristics, the hardness of a particular compound. In general,
the hardness of a homogeneous and uniform tread compound may be
both beneficial and detrimental to various performance
characteristics of a tire. For example, a harder tread compound may
be beneficial in terms of tread wear rate and rolling resistance,
when compared to a softer tread compound. However, the harder tread
compound may be more susceptible to an edge effect and/or damage
and have less wet traction than the softer tread compound.
[0034] Conversely, a softer tread compound may be less susceptible
to the edge effect and/or damage and have greater wet traction than
a harder tread compound. However, the softer tread compound may
have a greater tread wear rate and higher rolling resistance than
the harder tread compound. The cover sections 43 in accordance with
the present invention utilize a second harder and silica microflake
reinforced tread compound to take advantage of the benefits of the
harder and silicate microflake reinforced tread compound in the
area proximal to the circumferential grooves 41 and a softer tread
compound for the remaining portion of the tread 12.
[0035] Specifically, the stiffer second silicate microflake
reinforced compound of the cover sections 43 or 243 at the sides of
the circumferential grooves 41 or 241 may limit the deformation of
the first softer compound(s) of the adjacent tread ribs (i.e.,
"barrel" effect) thereby decreasing rolling resistance while
sacrificing little, if any, tread wear and/or traction (wet or dry)
characteristics. More specifically, the stiffer cover sections 43
or 243 decrease groove/rib deformation thereby decreasing
temperature build-up adjacent the grooves and decreasing rolling
resistance.
[0036] Further, the silicate microflakes of the cover sections 43
or cover layer 243 allow the second compound to be stiffer in the
circumferential direction than the radial direction of the tread
12. Thus, the cover sections 43 or 243 in accordance with the
present invention may decrease rolling resistance of a tire without
the structures by as much as 8%.
[0037] Typically the second compound for use as the above cover
sections 43 or 243 may be a composition comprising from 1 to 40 phr
(parts per weight, per 100 parts by weight of rubber) of silicate
microflakes having a thickness ranging from 0.02 microns to 40
microns and a diameter ranging from 2 microns to 250 microns.
Preferably the second compound comprises 3 phr to 25 phr of
silicate microflakes. More preferably the second compound comprises
5 phr to 10 phr silicate microflakes. Glass, mica, clay and/or
other suitable organic and/or inorganic microflakes may
alternatively be used in the second compound. Preferably the
silicate microflakes will have a thickness ranging from 0.2 to 30
microns and a diameter ranging from 6 to 100 microns. More
preferably the silicate microflakes will have a thickness ranging
from 0.4 to 20 microns and a diameter ranging from 10 to 60
microns.
[0038] The second compound having can contain 5 phr to 40 phr of
silicate microflakes and can have a thickness ranging from 0.4
microns to 20 microns and a diameter ranging from 10 microns to 60
microns and can be milled into a sheet and cut into tensile test
specimens. Tensile test specimens can be cut in two orientations,
one with the test pulling direction parallel with the milling
direction of the specimen, and one with the test pulling direction
perpendicular with the milling direction of the specimen. In this
way, the effect of microflake orientation (generally in the
direction of milling) and thus the anisotropy of the second
compound will be measured. The tensile samples will then be
measured for stress at various strains. A stress ratio, defined as
the (stress measured in the direction parallel to the milling
direction)/(stress measured in the direction perpendicular to the
milling direction) will then be calculated for each strain.
[0039] In another embodiment of the invention, the second compound
for use as the above cover layer 142 may be a rubber composition
comprising a diene based elastomer and from 5 phr to 40 phr of
silicate microflakes having a thickness ranging from 0.4 microns to
20 microns and a diameter ranging from 10 microns to 60 microns.
The silicate microflakes may have disposed on at least part of
their surface a composition comprising: an aliphatic fatty acid or
synthetic microcrystalline wax; a Bunte salt; a polysulfide
comprising the moiety --[S].sub.n or --[S].sub.o--Zn--[S].sub.p,
wherein each of o and p is 1-5, o+p=n, and n=2-6; and sulfur or a
sulfur donor.
[0040] The silicate microflakes may be provided in a batch with
natural rubber. Other microflakes, having similar stiffness,
anisotropy, and rubber adhesion, may also be used in accordance
with the present invention. Further, the microflakes of the above
specified dimensions may be blended with the rubber during
compounding/mixing.
[0041] An aliphatic fatty acid or synthetic microcrystalline wax
may be present in an amount ranging from 10 to 90 percent by
weight, based on the weight of the silicate microflakes, the fatty
acid or wax, the Bunte salt, and the polysulfide. The aliphatic
fatty acid may be stearic acid. The synthetic microcrystalline wax
may be polyethylene wax.
[0042] The Bunte salt may have the formula
(H).sub.m--(R.sup.1--S--SO.sub.3.sup.-M.sup.+)M.cndot.xH.sub.2O,
wherein m is 1 or 2, m' is 0 or 1, and m+m'=2; x is 0-3, M is
selected from Na, K, Li, 1/2 Ca, 1/2 Mg, and 1/3 Al, and R.sub.1 is
selected from C.sub.1-C.sub.12 alkylene, C.sub.1-C.sub.12
alkoxylene, and C.sub.7-C.sub.12 aralkylene. The Bunte salt may be
disodium hexamethylene-1,6-bis(thiosulfate) dihydrate. The amount
of the Bunte salt may range from 0.25 to 25 weight percent, based
on the weight of plain microflakes.
[0043] The polysulfide may be selected from the group consisting of
dicyclopentamethylene thiuram tetrasulfide,
bis-3-triethoxysilylpropyl tetrasulfide, alkyl phenol polysulfide,
zinc mercaptobenzothiazole, and 2-mercaptobenzothiazyl disulfide.
The amount of the polysulfide may range from 0.01 to 15 weight
percent, based on the weight of the plain microflakes.
[0044] The sulfur may be powdered sulfur, precipitated sulfur,
and/or insoluble sulfur. The sulfur donor may be tetramethylthiuram
disulfide, tetraethylthiuram disulfide, tetrabutylthiuram
disulfide, dipentamethylene thiuram hexasulfide, dipentamethylene
thiuram tetrasulfide, dithiodimorpholine, and/or mixtures thereof.
The amount of the sulfur or sulfur donor may range from 0.001 to 10
weight percent, based on the weight of the plain microflakes.
[0045] The combination of the Bunte salt, the polysulfide, and the
sulfur or sulfur donor may be present in an amount ranging from 0.5
to 40 percent by weight, based on the weight of the plain fibers.
In one embodiment, the combination of the Bunte salt, the
polysulfide, and the sulfur or sulfur donor is present in an amount
ranging from 1 to 20 percent by weight, based on the weight of the
plain fiber. In one embodiment, the combination of the Bunte salt,
the polysulfide, and the sulfur or sulfur donor is present in an
amount ranging from 2 to 8 percent by weight, based on the weight
of the plain microflake.
[0046] The rubber composition may be used with rubbers or
elastomers containing olefinic unsaturation. The phrases "rubber or
elastomer containing olefinic unsaturation" or "diene based
elastomer" are intended to include both natural rubber and its
various raw and reclaim forms, as well as various synthetic
rubbers. In this description, the terms "rubber" and "elastomer"
may be used interchangeably, unless otherwise prescribed. The terms
"rubber composition", "compounded rubber", and "rubber compound"
are used interchangeably to refer to rubber which has been blended
or mixed with various ingredients and materials and such terms as
are well known to those having skill in the rubber mixing or rubber
compounding art.
[0047] Representative synthetic polymers may be the
homopolymerization products of butadiene and its homologues and
derivatives, such as methylbutadiene, dimethylbutadiene, and
pentadiene, as well as copolymers, such as those formed from
butadiene or its homologues or derivatives with other unsaturated
monomers. Among the latter may be acetylenes (i.e., vinyl
acetylene), olefins (i.e., isobutylene, which copolymerizes with
isoprene to form butyl rubber), vinyl compounds (i.e., acrylic acid
or acrylonitrile, which polymerize with butadiene to form NBR),
methacrylic acid, and styrene (which polymerizes with butadiene to
form SBR), as well as vinyl esters and various unsaturated
aldehydes, ketones and ethers, e.g., acrolein, methyl isopropenyl
ketone, and vinylethyl ether.
[0048] Specific examples of synthetic rubbers may include neoprene
(polychloroprene), polybutadiene (including cis-1,4-polybutadiene),
polyisoprene (including cis-1,4-polyisoprene), butyl rubber,
halobutyl rubber (such as chlorobutyl rubber or bromobutyl rubber),
styrene/isoprene/butadiene rubber, copolymers of 1,3-butadiene or
isoprene with monomers such as styrene, acrylonitrile and methyl
methacrylate, as well as ethylene/propylene terpolymers, also known
as ethylene/propylene/diene monomer (EPDM), and in particular,
ethylene/propylene/dicyclopentadiene terpolymers. Additional
examples of rubbers which may be used include alkoxy-silyl end
functionalized solution polymerized polymers (SBR, PBR, IBR and
SIBR), and silicon-coupled and tin-coupled star-branched
polymers.
[0049] The rubber composition may also include up to 70 phr of
processing oil. Processing oil may be included in the rubber
composition as extending oil typically used to extend elastomers.
Processing oil may also be included in the rubber composition by
addition of the oil directly during rubber compounding. The
processing oil used may include both extending oil present in the
elastomers, and process oil added during compounding. Suitable
process oils include various oils as are known in the art,
including aromatic, paraffinic, naphthenic, vegetable oils, and low
PCA oils, such as MES, TDAE, SRAE and heavy naphthenic oils.
[0050] The rubber composition may further include from about 10 to
about 150 phr of silica. Siliceous pigments which may be used in
the rubber compound include conventional pyrogenic and precipitated
siliceous pigments (silica). Such conventional silicas might be
characterized, for example, by having a BET surface area, as
measured using nitrogen gas. The BET surface area may be in the
range of about 40 to about 600 square meters per gram. The
conventional silica may also be characterized by having a
dibutylphthalate (DBP) absorption value in a range of about 100 to
about 400, alternatively about 150 to about 300.
[0051] The conventional silica might be expected to have an average
ultimate particle size, for example, in the range of 0.01 micron to
0.05 micron, as determined by an electron microscope, although the
silica particles may be even smaller, or possibly larger, in size.
A wide variety of commercially available silicas can be used with
good results.
[0052] Commonly employed carbon blacks may be used as a
conventional filler in an amount ranging from 10 to 150 phr. The
carbon blacks may have iodine absorptions ranging from 9 to 145
g/kg and DBP number ranging from 34 to 150 cm.sup.3/100 g.
[0053] Other fillers may be used in the rubber composition
including, but not limited to, particulate fillers including ultra
high molecular weight polyethylene (UHMWPE), crosslinked
particulate polymer gels, and plasticized starch composite filler.
Such other fillers may be used in an amount ranging from 1 to 30
phr.
[0054] It may readily be understood by those having skill in the
art that the rubber composition would be compounded by methods
generally known in the rubber compounding art, such as mixing the
various sulfur-vulcanizable constituent rubbers with various
commonly used additive materials such as, for example, sulfur
donors, curing aids, such as activators and retarders and
processing additives, such as oils, resins including tackifying
resins and plasticizers, fillers, pigments, fatty acid, zinc oxide,
waxes, antioxidants and antiozonants and peptizing agents. As known
to those skilled in the art, depending on the intended use of the
sulfur vulcanizable and sulfur-vulcanized material (rubbers), the
additives mentioned above are selected and commonly used in
conventional amounts. Representative examples of sulfur donors
include elemental sulfur (free sulfur), an amine disulfide,
polymeric polysulfide and sulfur olefin adducts. In one embodiment,
the sulfur-vulcanizing agent is elemental sulfur. The
sulfur-vulcanizing agent may be used in an amount ranging from 0.5
to 8 phr, alternatively with a range of from 1.5 to 6 phr. Typical
amounts of tackifier resins, if used, comprise about 0.5 to about
10 phr, usually about 1 to about 5 phr. Typical amounts of
processing aids comprise about 1 to about 50 phr. Typical amounts
of antioxidants comprise about 1 to about 5 phr. Representative
antioxidants may be, for example, diphenyl-p-phenylenediamine and
others. Typical amounts of antiozonants comprise about 1 to 5 phr.
Typical amounts of fatty acids, if used, which can include stearic
acid comprise about 0.5 to about 3 phr. Typical amounts of zinc
oxide comprise about 2 to about 5 phr. Typical amounts of waxes
comprise about 1 to about 5 phr. In many cases microcrystalline
waxes are used. Typical amounts of peptizers comprise about 0.1 to
about 1 phr. Typical peptizers may be, for example,
pentachlorothiophenol and dibenzamidodiphenyl disulfide.
[0055] Accelerators may be used to control the time and/or
temperature required for vulcanization and to improve the
properties of the vulcanizate. A single accelerator system may be
used, i.e., primary accelerator. The primary accelerator(s) may be
used in total amounts ranging from about 0.5 to about 4 phr.
Combinations of a primary and a secondary accelerator may be used
with the secondary accelerator being used in smaller amounts, such
as from about 0.05 to about 3 phr, in order to activate and to
improve the properties of the vulcanizate. Combinations of these
accelerators may be expected to produce a synergistic effect on the
final properties and are somewhat better than those produced by use
of either accelerator alone.
[0056] In addition, delayed action accelerators may be used which
are not affected by normal processing temperatures, but produce a
satisfactory cure at ordinary vulcanization temperatures.
Vulcanization retarders might also be used. Suitable types of
accelerators that may be used are amines, disulfides, guanidines,
thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates and
xanthates.
[0057] The cover layer rubber formulation including the silicate
microflakes can be mixed utilizing a thermomechanical mixing
technique. The mixing of the cover layer rubber formulation can be
accomplished by methods known to those having skill in the rubber
mixing art. For example, the ingredients are typically mixed in at
least two stages; namely, at least one non-productive stage
followed by a productive mix stage. The final curatives including
sulfur-vulcanizing agents are typically mixed in the final stage
which is conventionally called the "productive" mix stage in which
the mixing typically occurs at a temperature, or ultimate
temperature, lower than the mix temperature(s) than the preceding
non-productive mix stage(s). The rubber, silica and sulfur
containing organosilicon, and carbon black, if used, are mixed in
one or more non-productive mix stages. The terms "non-productive"
and "productive" mix stages are well known to those having skill in
the rubber mixing art. The sulfur-vulcanizable rubber composition
containing the sulfur containing organosilicon compound,
vulcanizable rubber and generally at least part of the silica
should be subjected to a thermomechanical mixing step. The
thermomechanical mixing step generally comprises a mechanical
working in a mixer or extruder for a period of time suitable in
order to produce a rubber temperature between 140.degree. C. and
190.degree. C. The appropriate duration of the thermomechanical
working varies as a function of the operating conditions and the
volume and nature of the components. For example, the
thermomechanical working may be for a duration of time which is
within the range of about 2 minutes to about 20 minutes. It will
normally be preferred for the rubber to reach a temperature which
is within the range of about 145.degree. C. to about 180.degree. C.
and to be maintained at said temperature for a period of time which
is within the range of about 4 minutes to about 12 minutes. It will
normally be more preferred for the rubber to reach a temperature
which is within the range of about 155.degree. C. to about
170.degree. C. and to be maintained at said temperature for a
period of time which is within the range of about 5 minutes to
about 10 minutes.
[0058] The cover layer rubber formulation may be milled,
calendared, rolled, and/or extruded to form a sheet with the
silicate microflakes with an orientation in the direction of
processing, that is, a substantial portion of the silicate
microflakes will generally be oriented in a direction which is
consistent with, and parallel to, the material flow direction in
the processing equipment. The second rubber composition may have a
degree of anisotropy, that is, a modulus measured in a direction
consistent with the processing direction may be greater than that
measured in a direction perpendicular to the processing
direction.
[0059] FIG. 4 shows one such method, which entails extruding the
rubber formulation containing silicate microflakes with no
specified orientation 401 between rolls 402 to form the sheet with
the silicate microflakes aligned along the length of the sheet 403.
Another method is to use an extrusion machine 500 to extrude the
rubber formulation containing silicate microflakes with no
specified orientation 501 through an extrusion die 502 to form the
sheet with the silicate microflakes aligned along the length of the
sheet 503.
[0060] As stated above, located within each circumferential groove
41 or 141 and extending in an essentially circumferential direction
relative to the tread 12 is the cover layer 43 or 143. The
microflakes of the cover layer 43 or 143 may be substantially
oriented in the circumferential direction. By substantially
oriented, it is meant that the second compound for the reinforcing
structures 43 or 143 may comprise microflakes oriented at an angle
ranging from -20 degrees to +20 degrees with respect to the
circumferential direction along the tread 12 of the tire 10.
[0061] The example pneumatic tire for use with the present
invention may be a race tire, passenger tire, runflat tire,
aircraft tire, agricultural, earthmover, off-the-road, medium truck
tire, or any pneumatic or non-pneumatic tire. In one example, the
tire is a passenger or truck tire. The tire may also be a radial
ply tire or a bias ply tire.
[0062] Vulcanization of the example pneumatic tire may generally be
carried out at conventional temperatures ranging from about
100.degree. C. to 200.degree. C. Any of the usual vulcanization
processes may be used such as heating in a press or mold and/or
heating with superheated steam or hot air. Such tires can be built,
shaped, molded and cured by various methods which are known and are
readily apparent to those having skill in such art.
[0063] This invention is illustrated by the following examples that
are merely for the purpose of illustration and are not to be
regarded as limiting the scope of the invention or the manner in
which it can be practiced. Unless specifically indicated otherwise,
parts and percentages are given by weight.
Example 1
[0064] An extruded rubber sheet having silicate microflakes
dispersed therein oriented in such a manner as to be substantially
parallel with the surface of the sheet can be made in accordance
with the present invention by mixing natural rubber with about 7.5
phr of silicate microflakes having a thickness of about 5 microns
and a diameter of about 45 microns by using mixing techniques well
known in the art. In the mixture, the silicate microflakes will be
in no specific orientation, as shown by 401 in FIG. 4. The mixture
can then be extruded between rolls 402 to form a sheet of rubber
with the silicate microflakes aligned with the sheet of rubber as
shown by 403.
Example 2
[0065] Another embodiment of the present invention can be formed by
mixing natural rubber with about 7.5 phr of silicate microflakes
having a thickness of about 0.7 microns and a diameter of about 15
microns by using mixing techniques well known in the art. In the
mixture, the silicate microflakes will be in no specific
orientation, as shown by 501 in FIG. 5. The mixture can then be
extruded by use of a screw mechanism which forces the rubber
mixture through a die 502 thereby forming a sheet of rubber with
the silicate microflakes aligned with the sheet of rubber as shown
by 503.
Example 3
[0066] A tire in accordance with the present invention can be made
by positioning the sheet of rubber from either Example 1 or Example
2 around a tread cap of an uncured tire formed through methods well
known in the art. The tire assembly surrounded by the sheet of
rubber with silicate microflakes aligned along the length of the
sheet can be placed in a mold having the tread pattern formed
therein. The uncured tire can then be forced into a mold whereby
the sheet of rubber with silicate microflakes aligned along the
length of the sheet and the tread cap of the uncured tire if pushed
into the tread pattern of the mold to create a desired tread
pattern having grooves therein. The uncured tire can then be
vulcanized at 150.degree. C. by heating the mold. Once the tire is
sufficiently vulcanized to form a cured tire as understood by those
skilled in the art, the tire can be removed from the mold.
Example 4
[0067] The rubber compound containing silicate microflakes can be
removed from the ground contacting tread portion of the tire by
grinding away the outer tread surface of the tire. This can be
accomplished by grinding the road contacting surface of the tire of
Example 3 to a depth that is sufficient to substantially remove the
rubber containing the silicate microflakes from the ground
contacting tread surface of the tire.
[0068] While certain representative embodiments and details have
been shown for the purpose of illustrating the subject invention,
it will be apparent to those skilled in this art that various
changes and modifications can be made therein without departing
from the scope of the subject invention.
* * * * *