U.S. patent application number 10/298650 was filed with the patent office on 2003-07-24 for pneumatic radial tire.
Invention is credited to Kanenari, Daisuke, Kunugi, Tsuyoshi, Mama, Riichiro, Masaki, Takeo, Ohtani, Junichi, Shida, Zenichiro, Yamakawa, Kazuto.
Application Number | 20030136489 10/298650 |
Document ID | / |
Family ID | 17422669 |
Filed Date | 2003-07-24 |
United States Patent
Application |
20030136489 |
Kind Code |
A1 |
Kanenari, Daisuke ; et
al. |
July 24, 2003 |
Pneumatic radial tire
Abstract
A pneumatic tire comprising a rubber member containing a short
fiber (A') formed by the fibrillation of a short fiber (A) whose
cross section takes a sea-island structure essentially composed of
at least two polymers.
Inventors: |
Kanenari, Daisuke;
(Hiratsuka-shi, JP) ; Mama, Riichiro;
(Hiratsuka-shi, JP) ; Yamakawa, Kazuto;
(Hiratsuka-shi, JP) ; Masaki, Takeo;
(Hiratsuka-shi, JP) ; Shida, Zenichiro;
(Hiratsuka-shi, JP) ; Ohtani, Junichi;
(Hiratsuka-shi, JP) ; Kunugi, Tsuyoshi;
(Hiratsuka-shi, JP) |
Correspondence
Address: |
RADER, FISHMAN & GRAUER, PLLC
Suite 501
1233 20th Street, N.W.
Washington
DC
20036
US
|
Family ID: |
17422669 |
Appl. No.: |
10/298650 |
Filed: |
November 19, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10298650 |
Nov 19, 2002 |
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09774670 |
Feb 1, 2001 |
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09774670 |
Feb 1, 2001 |
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09159687 |
Sep 24, 1998 |
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6209603 |
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Current U.S.
Class: |
152/458 ;
152/525; 152/539; 152/547; 152/552 |
Current CPC
Class: |
B60C 9/1821 20130101;
B60C 13/00 20130101; B60C 15/06 20130101; Y10T 152/10765 20150115;
Y10T 152/10819 20150115; B60C 15/0607 20130101; Y10T 152/10846
20150115; B60C 11/005 20130101; Y10T 152/10513 20150115; Y10T
152/1081 20150115; B60C 11/00 20130101 |
Class at
Publication: |
152/458 ;
152/525; 152/539; 152/547; 152/552 |
International
Class: |
B60C 001/00; B60C
013/00; B60C 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 1997 |
JP |
9-265831 |
Claims
What is claimed is:
1. A pneumatic tire comprising a rubber member containing a
fibrillated short fiber A' formed by the fibrillation of a short
fiber A whose cross section takes a sea-island structure
essentially composed of at least two polymers, wherein the
fibrillated short fiber A' has an average diameter of 0.05 to 5.0
.mu.m.
2. A pneumatic tire according to claim 1, which comprises a carcass
layer bridging a pair of bead portions, a plurality of belt layers
lying in the tread portion on the outside of the carcass layer, and
compound sheets lying in both tire widthwise end portions of the
belt layers respectively, with the ratio b/a of the tire
circumferential modulus b of the compound sheets to the tire radial
modulus a thereof being adjusted to 1.2 or above by incorporating a
short fiber A' formed by the fibrillation of the above short fiber
A into the rubber constituting the compound sheets in a proportion
of 0.5 to 15 parts by weight per 100 parts by weight of the rubber
and orienting the fibrillated short fiber A' in a tire
circumferential direction.
3. A pneumatic tire according to claim 1, which comprises a carcass
layer bridging a pair of bead portions, a plurality of belt layers
lying in the tread portion on the outside of the carcass layer, and
compound sheets lying in both tire widthwise end portions of the
belt layers respectively, with the ratio of the tire
circumferential modulus (b) of the compound sheets to the tire
radial modulus (a) thereof (i.e., b/a ratio) being adjusted to 1.2
or above by incorporating a short fiber (A') formed by the
fibrillation of the above short fiber (A) and a composition which
comprises a short fiber (B) made of a thermoplastic polymer having
amido groups in the main chain and a matrix made of a rubber and/or
a polyolefin and wherein the short fiber (B) is dispersed in the
matrix and chemically bonded to the matrix into the rubber
constituting the compounds sheets in proportions of 0.5 to 10 parts
by weight of the fibrillated short fiber (A') and 1 to 15 parts by
weight of the short fiber, (B) per 100 parts by weight of the
rubber and orienting the fibrillated short is fiber (A') and the
short fiber (B) in a tire circumferential direction.
4. A pneumatic tire according to claim 2, wherein the fibrillated
short fiber (A') has an average diameter of 0.05 to 5.0 .mu.m.
5. A pneumatic tire according to claim 3, wherein the fibrillated
short fiber (A') has an average diameter of 0.05 to 5.0 .mu.m.
6. A pneumatic tire according to claim 5, wherein the short fiber B
has an average diameter of 0.05 to 5.0 .mu.m.
7. A pneumatic tire according to claim 2, wherein the compound
sheets have a width of at least 5% of the maximum belt width.
8. A pneumatic tire according to claim 2, wherein the compound
sheets have a thickness of 0.3 mm or above.
9. A pneumatic tire according to claim 1, wherein the ratio of the
tire circumferential modulus (b) of the tread to the tire radial
modulus (a) thereof (i.e., b/a ratio) is adjusted to 1.2 or above
by incorporating a short fiber (A') formed by the fibrillation of
the above short fiber (A) into the tread rubber in a proportion of
0.5 to 5 parts by weight per 100 parts by weight of the rubber and,
orienting the short fiber (A') in a tire circumferential direction,
and the groove area ratio of the tread is adjusted to 30 to
40%.
10. A pneumatic tire according to claim 1, wherein the ratio of the
tire circumferential modulus (b) of the tread to the tire radial
modulus (a) thereof (i.e., b/a ratio) is adjusted to 1.2 or above
by incorporating a short fiber (A') formed by the fibrillation of
the above short fiber (A) and a composition which comprises a short
fiber (B) made of thermoplastic polymer having amido groups in the
main chain and a matrix made of a rubber and/or a polyolefin and
wherein the short fiber (B) is dispersed in the matrix and
chemically bonded to the matrix into the tread rubber in
proportions of 0.5 to 10 parts by weight of the fibrillated short
fiber (A') and 1 to 15 parts by weight of the short fiber (B) per
100 parts by weight of the rubber and orienting the fibrillated
short fiber (Al) and the short fiber (B) in a tire circumferential
direction, while the groove area ratio of the tread is adjusted to
30 to 40%.
11. A pneumatic tire according to claim 1, wherein the tread
portion is constituted of at least two layers comprising a cap
tread and an under tread, and the ratio of the tire circumferential
modulus (b) of the under tread to the tire widthwise modulus (a)
thereof (i.e., b/a ratio) is adjusted to 1.5 or above by
incorporating a short fiber (A') formed by the fibrillation of the
above short fiber (A) into the rubber constituting the under tread
in a proportion the rubber and orienting the fibrillated short
fiber (A') in a tire circumferential direction.
12. A pneumatic tire according to claim 1, wherein the tread
portion is constituted of at least two layers comprising a cap,
tread and an under tread and the ratio of the tire circumferential
modulus (b) of the under tread to the tire widthwise modulus (a)
thereof (i.e., b/a ratio) is adjusted to 1.5 or above by
incorporating a short fiber (A') formed by the fibrillation of the
above short fiber (A) and a composition which comprises a short
fiber (B) made of a thermoplastic polymer having amido groups in
the main chain and a matrix made of a rubber and/or a polyolefin
and wherein the short fiber (B) is dispersed in the matrix and
chemically bonded to the matrix into the rubber constituting the
under tread in proportions of 1 to 12 parts by weight of the
fibrillated short fiber (A') and 1 to 10 parts by weight of the
short fiber (B) per 100 parts by weight of the rubber and orienting
the fibrillated short fiber (A') and the short fiber (B) in a tire
circumferential direction.
13. A pneumatic tire according to claim 1, wherein at least a part
of the sidewall is made from a rubber composition containing 0.5to
15 parts by weight of a short fiber (A') formed by the fibrillation
of the above short fiber (A) per 100 part by weight of the
rubber.
14. A pneumatic tire according to claim 1, wherein at least a part
of the sidewall is made from a rubber composition containing a
short fiber (A') formed by the fibrillation of the above short
fiber (A) and a composition which comprises a short fiber (B) made
of a thermoplastic polymer having amido groups in the main chain
and a matrix made of a rubber and/or a polyolefin and wherein the
short fiber (B) is dispersed in the matrix and chemically bonded to
the matrix in proportions of 0.5 to 10 parts, by weight of the
fibrillated short fiber (A') and 1 to 15 parts by weight of the
short fiber (B) per 100 parts by weight of the rubber.
15. A pneumatic tire according to claim 1, which comprises a
carcass layer containing a plurality of carcass cords in a state
arranged in the tire radial direction and bridging a pair of bead
portions with both tire widthwise end portions of the carcass layer
wound up around the bead cores respectively from the tire inner
side to the tire outer side, and short fiber reinforced layers
lying at least in the wound-up end portions of the carcass layer,
with the ratio of the tire circumferential modulus (b) of the short
fiber reinforced layers to the tire radial modulus (a) thereof
(i.e., b/a ratio) being adjusted to 1.2 or above by incorporating a
short fiber (A') formed by the fibrillation of the above short
fiber (A) into the rubber constituting the short fiber reinforced
layers in a proportion of 0.5 to 15 parts by weight the fibrillated
short fiber (A') in a tire circumferential direction.
16. A pneumatic tire according to claim 1, which comprises a
carcass layer containing a plurality of carcass cords in a state
arranged in the tire radial direction and bridging a pair of bead
portions with both tire width wise end portions of the carcass
layer wound up around the bead cores respectively from the tire
inner side to the tire outer side, and short fiber reinforced
layer's lying at least in the wound up end portions of the carcass
layer, with the ratio of the tire circumferential modulus (b) of
the short fiber reinforced layers to the tire radial modulus (a)
thereof (i.e., b/a ratio) being adjusted to 1.2 or above by
incorporating a short fiber (A') formed by the fibrillation of the
above short fiber (A) and a composition which comprises a short
fiber (B) made of a thermoplastic polymer having amido groups in
the main chain and a matrix made of a rubber and/or a polyolefin
and wherein the short fiber (B) is dispersed in the matrix and
chemically bonded to the matrix into the rubber constituting the
short fiber reinforced layers in proportions of 0.5 to 10 parts by
weight of the fibrillated short fiber (A') and 1 to 15 parts by
weight of the short fiber (B) per 100 parts by weight of the rubber
and orienting the fibrillated short fiber (A) and the short fiber
(B) in a tire circumferential direction.
17. A pneumatic tire according to claim 1, comprising bead fillers
located on the outer peripheral sides of the bead cores
respectively, wherein the bead fillers are made of a rubber
composition containing a short fiber (A') formed by the
fibrillation of the above short fiber (A) in a proportion of 3 to
15 parts by weight per 100 parts by weight of the rubber in a state
oriented in a direction perpendicular to the tire radial direction,
whereby the ratio of the storage modulus (b) of the bead fillers in
the direction of orientation of the short fiber to the tire radial
storage modulus (a) thereof (i.e., b/a ratio) is adjusted to 4 to
10.
18. A pneumatic tire according to claim 1, comprising bead fillers
located on the outer peripheral sides of the bead cores
respectively, wherein the bead fillers are made of a rubber
composition containing a short fiber (A') formed by the
fibrillation of the above short fiber (A) and a composition which
comprises a short fiber (B) made of a thermoplastic polymer having
amido groups in the main chain and a matrix made of a rubber and/or
a polyolefin and wherein the short fiber (B) is dispersed in the
matrix and chemically bonded to the matrix in proportions of 3 to
10 parts by weight of the fibrillated short fiber (A') and 1 to 15
parts by weight of the short fiber (B) per 100 parts by weight in a
state oriented in a direction perpendicular to the tire radial
direction, whereby the ratio of the storage modulus (b) of the bead
fillers in the direction of orientation of the short fiber to the
tire radial storage modulus (a) thereof (i.e., b/a ratio) is
adjusted to 4 to 10.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a pneumatic tire being
improved in various tire performance parameters, which is
effectively reinforced by incorporating a specific short fiber into
a rubber member constituting the tire so as to satisfy the basic
requirements for a tire.
[0002] As a means for reinforcing the rubber member constituting a
tire, it has been a common practice to embed reinforcement cords in
the rubber or to use a high-hardness rubber. When the rigidity of
the rubber member was uniformly changed to improve a specific tire
performance, however, a problem occurred that the other tire
performance parameters were lowered.
[0003] With respect to a pneumatic radial tire, for example, it has
been known that road noise can be reduced by enhancing the rigidity
of the shoulder portions near the belt edges. It has therefore been
a general practice to insert sheets or fillers made of a high
hardness compound under both belt end portions to thereby enhance
the rigidity of the shoulder portions. When such sheets or fillers
made of a high-hardness compound are used, however, the basic
performance parameters such as comfortableness in riding and
stability in steering are changed by enhancement in the rigidity of
the shoulder portions, even though road noise can be reduced.
[0004] Further, attempts have been made to enhance selectively the
modulus of a rubber member constituting a tire in a specific
direction by incorporating a short fiber made of nylon or the like
into the rubber member and orienting it in the specific direction.
However, the short fibers of the prior art have failed in attaining
such effective reinforcement as to satisfy the basic requirements
for a tire.
SUMMARY OF THE INVENTION
[0005] The first object of the present invention is to provide a
pneumatic tire that is so effectively reinforced by incorporating a
specific short fiber into a rubber member constituting the tire as
to satisfy the basic requirements for a tire.
[0006] The second object of the present invention is to provide a
pneumatic tire which is reduced in road noise by the use of the
above specific short fiber with the basic performance parameters
such as comfortableness in riding and stability in steering being
kept at high levels.
[0007] The third object of the present invention is to provide a
pneumatic tire which can exhibit excellent braking performance both
on a dry road surface and on a wet road surface by virtue of the
use of the above specific short fiber.
[0008] The fourth object of the present invention is to provide a
pneumatic tire comprising an under tread made of a rubber
exhibiting a small energy loss (for lowering rolling resistance),
which tire has a reduced nonuniformity of gauge resulting from
rubber flow occurring during the molding of the tire with
vulcanization and improved stability in steering, by virtue of the
use of the above specific short fiber.
[0009] The fifth object of the present invention is to provide a
pneumatic tire that is reduced in the sidewall gauge by the use of
the above specific short fiber with a reduction in the weight
without impairing the resistance of the sidewall to external
damage.
[0010] The sixth object of the present invention is to provide a
pneumatic tire that is improved in durability by the use of the
above specific short fiber with a decrease in the rubber volume of
the bead portions.
[0011] The seventh object of the present invention is to provide a
pneumatic tire which is reduced in the weight and improved in
comfortableness in riding by the use of the above specific short
fiber with the stability in steering being kept at a level
equivalent or superior to that of a tire provided with steel
reinforcements in the neighborhood of the bead fillers.
[0012] The pneumatic tire of the present invention achieving the
above first object is one comprising a rubber member containing a
short fiber (A') formed by the fibrillation of a short fiber (A)
whose cross section takes a sea-island structure essentially
composed of at least two polymers.
[0013] When the above fibrillated short fiber (A') is incorporated
into the rubber member, the short fiber (A') enhances the modulus
of the member at low elongation by leaps and bounds to exhibit
excellent reinforcing effect.
[0014] The term "modulus" used in this specification refers to
"modulus at 20% elongation" (hereinafter referred to merely as "20%
modulus"). A tire is generally used in the strain range of 50% or
below, so that the characteristics of a rubber at low elongation
based on 20% modulus highly correlate with tire performance
parameters. Thus, a tire can be reinforced effectively by enhancing
the 20% modulus. Accordingly, the reinforcement of a tire with the
above short fiber makes it possible to improve various tire
performance parameters required depending on the use of the
tire.
[0015] Such 20% modulus can be determined according to the method
of tensile test at low elongations as stipulated in JIS K6301. This
method comprises using a test piece having a width of 5 mm, a
length of 100 mm, a thickness of 2 mm and a distance of 40 mm
between two gage marks, stretching this test piece preliminarily
twice at a rate of 45+15 mm/min by 1.5 times the elongation (20%)
to be subjected in the test, stretching the resulting test piece by
20% at the same rate as that employed in the preliminary stretching
and keeping the same in the state thus stretched, and measuring the
load after the lapse of 30 seconds. The modulus at 20% elongation
(20% modulus) can be determined by the following formula. The
measurement of the load is repeated generally four times and the
average of the four values is used.
.sigma..sub.20=F.sub.20/S
[0016] .sigma..sub.20 modulus at 20% elongation (MPa)
[0017] F.sub.20: load at 20% elongation (N)
[0018] S sectional area of test piece
[0019] A pneumatic tire of the present invention achieving the
above second object is a pneumatic radial tire which comprises a
carcass layer-bridging a pair of, i.e., lefthand and righthand bead
portions and a plurality of belt layers lying in the tread portion
on the outside of the carcass layer and which further comprises
compound sheets lying in both tire widthwise end portions of the
belt layers respectively, with the ratio of the tire
circumferential modulus (b) of the compound sheets to the tire
radial modulus (a) thereof (i.e., b/a ratio) being adjusted to 1.2
or above by incorporating a short fiber (A') formed by the
fibrillation of a short fiber (A) whose cross section takes a
sea-island structure essentially composed of at least two polymers
into the rubber constituting the compound sheets in a proportion of
0.5 to 15 parts by weight per 100 parts by weight of the rubber and
orienting the fibrillated short fiber (A') in a tire
circumferential direction.
[0020] Another pneumatic tire of the present invention achieving
the above second object is a pneumatic radial tire which comprises
a carcass layer bridging a pair of, i.e., lefthand and righthand
bead portions and a plurality of belt layers lying in the tread
portion on the outside of the carcass layer and which further
comprises compound sheets lying in both tire widthwise end portions
of the belt layers respectively, with the ratio of the tire
circumferential modulus (b) of the compound sheets to the tire
radial modulus (a) thereof (i.e., b/a ratio) being adjusted to 1.2
or above by incorporating a short fiber (A') formed by the
fibrillation of a short fiber (A) whose cross section takes a
sea-island structure essentially composed of at least two polymers
and a composition comprising a short fiber (B) made of a
thermoplastic polymer having amido groups in the main chain and a
matrix made of a rubber and/or a polyolefin wherein the short fiber
(B) is dispersed in the matrix and chemically bonded to the matrix
into the rubber constituting the compound sheets in proportions of
0.5 to 10 parts by weight of the fibrillated short fiber (A') and 1
to 15 parts by weight of the short fiber (B) per 100 parts by
weight of the rubber and orienting the fibrillated short fiber (A')
and the short fiber (B) in a tire circumferential direction.
[0021] In the above cases wherein such anisotropic rubber compound
sheets that the tire circumferential modulus (b) is larger than the
tire radial modulus (a) by a specific factor or above are laid in
both end portions of the belt layers, the rigidities in the tire
width direction and in the tire radial direction (perpendicular to
the tire rotating shaft) can be adjusted to levels equivalent to
those of the prior art with an enhancement in the tire
circumferential rigidity of the shoulder portions' near the belt
edges. This makes it possible to reduce road noise with the basic
performance parameters such as comfortableness in riding and
stability in steering being kept at high-levels.
[0022] A pneumatic tire of the present invention achieving the
above third object is one wherein the ratio of the tire
circumferential modulus (b) of the tread to the tire radial modulus
(a) thereof (i.e., b/a ratio) is adjusted to 1.2 or above by
incorporating a short fiber (A') formed by the fibrillation of a
short fiber (A) whose cross section takes a sea-island structure
essentially composed of at least two polymers into the tread rubber
in a proportion of 0.5 to 15 parts by weight per 100 parts by
weight of the rubber and orienting the short fiber (A') in a tire
circumferential direction, and the groove area ratio of the tread
is adjusted to 30 to 40%.
[0023] Another pneumatic tire of the present invention, achieving
the above third object is one wherein the ratio of the tire
circumferential modulus (b) of the tread to the tire radial modulus
(a) thereof (i.e., b/a ratio) is adjusted to 1.2 or above by
incorporating a short fiber (A') formed by the fibrillation of a
short fiber (A) whose cross section takes a sea-island structure
essentially composed of at least two polymers and a composition
comprising a short fiber (B) made of a thermoplastic polymer having
amido groups in the main chain and a matrix made of a rubber and/or
a polyolefin wherein the short fiber (B) is dispersed in the matrix
and chemically bonded to the matrix into the tread rubber in
proportions of 0.5 to 10 parts by weight of the fibrillated short
fiber (A') and 1 to 15 parts by weight of the short fiber (B) per
100 parts by weight of the rubber and orienting the fibrillated
short fiber (A') and the short fiber (B) in a tire circumferential
direction and the groove area ratio of the tread is adjusted to 30
to 40%.
[0024] Although a pneumatic tire having a larger ground contacting
area is more advantageous in braking performance on a dry road
surface, it is also required to have sufficient groove area enough
to secure satisfactory drainage performance on a wet road surface.
Therefore, there is a limit to the improvement of both braking
performance on a dry road surface and that on a wet road surface in
a well-balanced state by changing the groove area ratio.
[0025] In the above cases wherein the groove area ratio of the
tread is limited to the above range and such an anisotropic rubber
tread that the tire circumferential modulus (b) is larger than the
tire radial modulus (a) by a specific factor or above is employed,
only the tire circumferential rigidity of the tread can selectively
be enhanced. At the same time, sufficient actual ground-contacting
area is secured by controlling the tire radial rigidity of the
tread to a conventional level or below. Thus, the braking
performance on a dry road surface can well meet with that on a wet
road surface at high levels.
[0026] A pneumatic tire of the present invention achieving the
above fourth object is one wherein the tread portion is constituted
of at least two layers comprising a cap tread and an under tread,
and the ratio of the tire circumferential modulus (b) of the under
tread to the tire widthwise modulus (a) thereof (i.e., b/a ratio)
is adjusted to 1.5 or above by incorporating a short fiber (A')
formed by the fibrillation of a short fiber (A) whose cross section
takes a sea-island structure essentially composed of at least two
polymers into the rubber constituting the under tread in a
proportion of 1 to 15 parts by weight per 100 parts by weight of
the rubber and orienting the fibrillated short fiber (A') in a tire
circumferential direction.
[0027] Another pneumatic tire of the present invention achieving
the above fourth object is one wherein the tread is constituted of
at least two layers comprising a cap tread and an under tread, and
the ratio of the tire circumferential modulus (b) of the under
tread to the tire widthwise modulus (a) thereof (i.e., b/a ratio)
is adjusted to 1.5 or above by incorporating a short fiber (A')
formed by the fibrillation of a short fiber (A) whose cross section
takes a sea-island structure essentially composed of at least two
polymers and a composition comprising a short fiber (B) made of a
thermoplastic polymer having amido groups in the main chain and a
matrix made of a rubber and/or a polyolefin wherein the short fiber
(B) is dispersed in the matrix and chemically bonded to the matrix
into the rubber constituting the under tread in proportions of 1 to
12 parts by weight of the fibrillated short fiber (A') and 1 to 10
parts by weight of the short fiber (B) per 100 parts by weight of
the rubber and orienting the fibrillated short fiber (A') and the
short fiber (B) in a tire circumferential direction.
[0028] For the purpose of meeting the recent demand for improved
fuel consumption of vehicles, various attempts were made to reduce
the rolling resistance of a tire. As a technique of reconciling
improved fuel consumption with traveling performance on a wet road
surface, for example, it has been a common practice to employ a
two-layer tread constituted of a cap tread and an under tread to
thereby decrease the volume of the cap tread exhibiting a large
energy loss. In this practice, specifically, a rubber excellent in
wet performances is used as the cap tread and a rubber exhibiting a
small energy loss is used as the under tread.
[0029] When the content of carbon black in the under tread is
lowered in order to lower the energy loss of the under tread,
however, the resulting rubber gives too soft of a vulcanizate to
attain satisfactory stability in steering. On the other hand, when
a butadiene rubber excellent in impact resilience is incorporated
into the under tread, the resulting under tread has such a low
green viscosity as to cause rubber flow easily in pressing against
the tread the groove-forming skeletons present on the inner surface
of a mold during the molding of the tire with vulcanization.
Therefore, the under tread becomes too thin in the portions located
under grooves and becomes too thick in the portions located under
blocks. Thus, the tire provided with an under tread containing a
butadiene rubber or the like is disadvantageous in that the under
tread comes out to the surface in the last stage of wear to result
in poor traction performance.
[0030] In the above cases wherein the ratio of the tire
circumferential modulus (b) of the under tread to the tire
widthwise modulus (a) thereof (i.e., b/a ratio) is adjusted to 1.5
or above by incorporating a short fiber (A') formed by the
fibrillation of a short fiber (A) whose cross section takes a
sea-island structure essentially composed of at least two polymers
in a specific proportion and orienting the short fiber (A') in a
tire circumferential direction, the molding of the tire with
vulcanization exhibits little rubber flow thereby obtained an
improved uniformity in the under tread gauge, even if a rubber
exhibiting a low energy loss is used as the under tread for the
purpose of reducing the rolling resistance of the tire. After the
vulcanization, the fibrillated short fiber (A') is present in the
under tread in a state oriented in a tire circumferential direction
to exhibit a high reinforcing effect, thus improving the stability
in steering.
[0031] The above fibrillated short fiber (A') has L excellent
features as compared with the nylon short fiber and carbon black
according to the prior art. Specifically, a rubber containing the
fibrillated short fiber (A') even in a large amount suffers little
from the rise of tan .delta., even though a rubber containing
carbon black in an amount increased for, the purpose of enhancing
the hardness of the under tread exhibits an enhanced tan .delta.,
with a rise in the hardness. Further, a rubber containing the
fibrillated short fiber (A') even in a large amount has a slightly
increased green viscosity, even though a rubber containing a large
amount of the nylon short fiber of the prior art exhibits too high
a green viscosity to exhibit satisfactory processability in
kneading and extrusion. Therefore, the incorporation of the
fibrillated short fiber (A') into a rubber can enhance the green
modulus of the rubber not only in the grain direction (direction of
orientation of the fiber) but also in the reverse grain direction
(perpendicular to the direction of orientation of the fiber). Thus,
the incorporation of the fibrillated short fiber (A') into an under
tread gives an under tread which is hard and exhibits a low heat
build-up. Further, this under tread is therefore inhibited from
rubber flow during the vulcanization of the tire by virtue of its
high green strength, in spite of its being more excellent in
processability than the one containing the nylon short fiber of the
prior art. Furthermore, the incorporation of the fibrillated short
fiber (A') also brings about the effect of inhibiting the rubber
compound from cold flow during the storage.
[0032] A pneumatic tire of the present invention achieving the
above fifth object is one wherein at least a part of the sidewall
is made of a rubber composition containing 0.5 to 15 parts by
weight of a short fiber (A') formed by the fibrillation of a short
fiber (A) whose cross section takes a sea-island structure
essentially composed of at least two polymer.
[0033] Another pneumatic tire of the present invention achieving
the above fifth object is one wherein at least a part of the
sidewall is made of a rubber composition containing a short fiber
(A') formed by the fibrillation of a short fiber (A) whose cross
section takes a sea-island structure essentially composed of at
least two polymers and a composition comprising a short fiber (B)
made of a thermoplastic polymer having amido groups in the main
chain and a matrix made of a rubber and/or a polyolefin wherein the
short fiber (B) is dispersed in the matrix and chemically bonded to
the matrix in proportions of 0.5 to 10 parts by weight of the
fibrillated short fiber (A') and 1 to 15 parts by weight of the
short fiber (B) per 100 parts by weight of the rubber.
[0034] The resistance of a pneumatic tire to external damage is
lowered, when the gauge of the sidewall rubber is merely decreased
for the purpose of reducing the weight. Although a sidewall can be
reinforced by adding nylon short fiber to the rubber constituting
the sidewall, the reinforcement with nylon fiber results in an
unsatisfactory reinforcing effect. Thus, no satisfactory resistance
to external damage can be secured, when the weight of a tire is
reduced by decreasing the sidewall gauge.
[0035] In the above cases wherein a short fiber (A') formed by the
fibrillation of a short fiber (A) whose cross section takes a
structure essentially composed of at least two polymers is
incorporated into the sidewall rubber in a specific proportion, the
fibrillated short fiber (A') enhances the modulus at low elongation
by leaps and bounds to exhibit an excellent reinforcing effect,
which makes it possible to secure satisfactory resistance to
external damage even when the weight of a tire is reduced by
decreasing the sidewall gauge.
[0036] It is preferable that the fibrillated short fiber (A') be
oriented in a direction parallel to the sidewall face. The
fibrillated short fiber (A') may be oriented in any state in the
tire circumferential and radial directions, as far as it is
oriented in a direction parallel to the sidewall face. For example,
the short fiber (A') may be oriented in a specific direction (such
as circumferential direction) or arrange at random. The maximum
reinforcing effect of the fibrillated short fiber (A') can be
exhibited, when the fiber (A') is oriented in such a state.
[0037] A pneumatic tire of the present invention achieving the
above sixth object is a heavy-duty pneumatic radial tire comprising
a carcass layer which contains a plurality of carcass cords in a
state arranged in the tire radial direction and bridges a pair of,
i.e., lefthand and righthand bead portions with both tire widthwise
end portions of the carcass layer wound up around the bead cores
respectively from the tire inner side to the tire outer side, and
which further comprises short fiber reinforced layers lying at
least in the wound-up end portions of the carcass layer, with the
ratio of the tire circumferential modulus (b) of the short fiber
reinforced layers to the tire radial modulus (a) thereof (i.e., b/a
ratio) being adjusted to 1.2 or above by incorporating a short
fiber (A') formed by the fibrillation of a short fiber (A) whose
cross section takes a sea-island structure essentially composed of
at least two polymers into the rubber constituting the short fiber
reinforced layers in a proportion of 0.5 to 15 parts by weight per
100 parts by weight of the rubber and orienting the short fiber
(A') in a tire circumferential direction.
[0038] Another pneumatic tire of the present invention achieving
the above sixth object is a heavy-duty pneumatic radial tire
comprising a carcass layer which contains a plurality of carcass
cords in a state arranged in the tire radial direction, bridges a
pair of, i.e., lefthand and righthand bead portions with both tire
widthwise end portions of the carcass layer wound up around the
bead cores respectively from the tire inner side to the tire outer
side, and further comprises short fiber reinforced layers lying at
least in the wound-up end portions of the carcass layer, with the
ratio of the tire circumferential modulus (b) of the short fiber
reinforced layers to the tire radial modulus (a) thereof (i.e., b/a
ratio) being adjusted to 1.2 or above by incorporating a short
fiber (A') formed by the fibrillation of a short fiber (A) whose
cross section takes a sea-island structure essentially composed of
at least two polymers and a composition comprising a short fiber
(B) made of a thermoplastic polymer having amido groups in the main
chain and a matrix made of a rubber and/or a polyolefin wherein the
short fiber (B) is dispersed in the matrix and chemically bonded to
the matrix into the rubber constituting the short fiber reinforced
layers in proportions of 0.5 to 10 parts by weight of the
fibrillated short fiber (A') and 1 to 15 parts by weight of the
short fiber (B) per 100 parts by weight of the rubber and orienting
the fibrillated short fiber (A') and the short fiber (B) in a tire
circumferential direction.
[0039] There have been known heavy-duty pneumatic radial tires
wherein reinforcing layers containing steel cords or organic fiber
cords are laid in the bead portions for the purpose of enhancing
durability. Even when such a reinforcing structure is formed
however, it is still difficult to inhibit the delamination among
cords occurring in the wound-up end portions of the carcass
layer.
[0040] Precisely, the wound-up end portions of the carcass layer
contain parts wherein the carcass cords are not bonded to the
rubber, so that cracks are initiated in such parts and then grown
to result in the delamination among carcass cords. Although it has
been known that the wound-up end portions of the carcass layer can
be reinforced with rubber reinforcement layers, such reinforcement
not only fails in attaining a satisfactory effect, but also brings
about an increase in the weight.
[0041] In the above cases wherein such anisotropic short fiber
reinforced rubber layers that the tire circumferential modulus (b)
is larger that the tire radial modulus (b) by a specific factor or
above are laid in the wound-up end portions of the carcass layer,
the cords arranged in the tire radial direction are effectively
inhibited from moving in a tire circumferential direction, so that
the stress concentration in the wound-up end portions can be
relaxed with a decrease in the rubber volume of the bead portions
to thereby inhibit the delamination among cords and thus enhance
the durability of the tire. Additionally, when a steel cord
reinforced layer containing a plurality of steel cords in a state
arranged in the tire radial direction is further laid in such a way
as to lie along the carcass layer in the bead portions, the
delamination among cords in the upper end portions of the steel
cord reinforced layer can also be inhibited by laying the short
fiber reinforced layers in the upper end portions of the steel cord
reinforced layer.
[0042] A pneumatic tire of the present invention achieving the
above seventh object is a pneumatic radial tire comprising bead
fillers located on the outer peripheral sides of the bead cores
respectively, wherein the bead fillers are made of a rubber
composition containing a short fiber (A') formed by the
fibrillation of a short fiber (A) whose cross section takes a
sea-island structure essentially composed of at least two polymers
in a proportion of 3 to 15 parts by weight per 100 parts by weight
of the rubber in a state oriented in a direction perpendicular to
the tire radial direction, whereby the ratio of the storage modulus
(b) of the bead fillers in the direction of orientation of the
short fiber to the tire radial storage modulus (a) thereof (i.e.,
b/a ratio) is adjusted to 4 to 10.
[0043] Another pneumatic tire of the present invention achieving
the above seventh object is a pneumatic radial tire comprising bead
fillers located on the outer peripheral sides of the bead cores
respectively, wherein the bead fillers are made of a rubber
composition containing a short fiber (A') formed by the
fibrillation of a short fiber (A) whose cross section takes a
sea-island structure essentially composed of at least two polymers
and a composition comprising a short fiber (B) made of a
thermoplastic polymer having amido groups in the main chain and a
matrix made of a rubber and/or a polyolefin wherein the short;
fiber (B) is dispersed in the matrix and chemically bonded to the
matrix in proportions of 3 to 10 parts by weight of the fibrillated
short fiber (A') and 1 to 15 parts by weight of the short fiber (B)
per 100 parts by weight in a state oriented in a direction
perpendicular to the tire radial direction, whereby the ratio of
the storage modulus (b) of the bead fillers in the direction of
orientation of the short fiber to the tire radial storage modulus
(a) thereof (i.e., b/a ratio) is adjusted to 4 to 10.
[0044] In improving the stability in steering of a pneumatic radial
tire having an aspect ratio of 60% or below, means for laying steel
reinforcements in the neighborhood of the bead fillers is generally
employed. This is because the rigidity of the bead portions cannot
sufficiently be enhanced merely by enhancing the rigidity of the
bead fillers. When such steel reinforcements are laid in the bead
portions, however, the resulting tire is significantly deteriorated
in comfortableness in riding owing to its too high tire radial
rigidity and is increased in weight. On the other hand, when no
steel reinforcement is used, the resulting tire is poor in
stability in steering, because of the bead portions being too
soft.
[0045] In the above cases wherein anisotropic rubber bead fillers
which contain the fibrillated short fiber (A') in a state oriented
in a direction perpendicular to the tire radial direction and in
which the storage modulus (b) in the direction of orientation of
the short fiber is larger than the tire radial storage modulus (a)
by a specific factor or above are laid on the outer peripheral
sides of the bead cores, the rigidity of the bead portions in a
direction perpendicular to the tire radial direction can be
enhanced without any substantial change in the rigidity of the bead
portions in the tire radial direction. Accordingly, the use of such
bead fillers makes it possible to secure not only stability in
steering equivalent or superior to that of a tire provided with
steel reinforcements in the neighborhood of the bead fillers but
also comfortableness in riding and a light weight equivalent to
those of a tire not provided with any steel reinforcement.
[0046] The above anisotropy of the bead fillers can be attained by
orienting the fibrillated short fiber (A') in a direction
perpendicular to the tire radial direction. The short fiber (A')
may be oriented in a tire circumferential direction or the tire
rotating shaft direction. The orientation in a tire circumferential
direction is preferable. Alternatively, two-layer bead fillers
constituted of two layers laminated in the tire rotating shaft
direction may be employed, one of the layers containing the short
fiber in a state oriented in the tire circumferential direction and
the other layer containing it in a state oriented in the tire
rotating shaft direction.
[0047] It is preferable that the above anisotropic constitution of
bead fillers be applied to pneumatic radial tires having aspect
ratios of 60% or below. The application to such oblate tires brings
about more remarkable functions and effects.
[0048] In this specification, each storage modulus value is one
determined with respect to a test piece having a width of 5 mm, a
length of 20 mm and a thickness of 2 mm by using a viscoelasticity
spectrometer at a strain of 5.+-.1%, a frequency of 20 Hz and a
temperature of 20.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] FIG. 1 is a meridional sectional view showing an example of
the pneumatic radial tire according to the first embodiment of the
present invention;
[0050] FIG. 2 is a meridional sectional view showing the essential
portion of a modification example of the pneumatic radial tire
according to the first embodiment of the present invention;
[0051] FIG. 3 is a meridional sectional view showing the essential
portion of another modification example of the pneumatic radial
tire according to the first embodiment of the present
invention.
[0052] FIG. 4 is a meridional half sectional view showing an
example of the pneumatic radial tire according to the second
embodiment of the present invention;
[0053] FIG. 5 is a meridional half sectional view showing the
pneumatic tire according to the third embodiment of the present
invention;
[0054] FIG. 6 is a meridional half sectional view showing an
example of the pneumatic tire according to the fourth embodiment of
the present invention;,
[0055] FIG. 7 is a meridional half sectional view showing a
modification example of the pneumatic tire according to the fourth
embodiment of the present invention;
[0056] FIG. 8 is a meridional half sectional view showing another
modification example of the pneumatic tire according to the fourth
embodiment of the present invention;
[0057] FIG. 9 is a sectional view showing an example of the bead
portion of the heavy-duty pneumatic radial tire according to the
fifth embodiment of the present invention;
[0058] FIG. 10 is a perspective view showing the wound-up portion
of the carcass layer shown in FIG. 9;
[0059] FIG. 11 is a sectional view showing a modification example
of the bead portion of the heavy duty pneumatic radial tire
according to the firth embodiment of the present invention;
[0060] FIG. 12 is a meridional half sectional showing an example of
the pneumatic radial tire according to the sixth embodiment of the
present invention;
[0061] FIG. 13 is a perspective sectional view showing an example
of the bead filler according to the embodiment shown in FIG. 12;
and
[0062] FIG. 14 is a perspective sectional view showing modification
example of the bead filler according to the embodiment shown in
FIG. 12; and
[0063] FIG. 15 is a perspective sectional view showing another
modification example of the bead filler according to the embodiment
shown in FIG. 12.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0064] FIG. 1 shows an example of the pneumatic radial tire
according to the first embodiment of the present invention. In FIG.
1, a carcass layer 12 containing a plurality of reinforcement cords
in a state arranged in the radial direction bridges a pair of,
i.e., lefthand and righthand bead portions 11, 11. Both tire
widthwise end portions of the carcass layer 12 are wound up around
the bead cores 13 respectively from the tire inner side to the tire
outer side.
[0065] Two belt layers 15a and 15b each containing a plurality of
steel cords are laid in the tread portion 14 on the outside of the
carcass layer 12. These belt layers 15a and 15b are laid in such a
way that the reinforcement cords are arranged obliquely to the tire
circumferential direction and that the reinforcement cords
contained in one of the layers 15a and 15b cross those contained in
the other layer. In the inner belt layer 15a, the angle of cord is
adjusted to 15 to 30.degree. to the tire circumferential direction,
while in the outer belt layer 15b, the angle of cord is adjusted to
15 to 30.degree. thereto.
[0066] Compound sheets 16 are laid in the tire widthwise end
portions of the belt layers 15a and 15b respectively. It is
preferable that these compound sheets 16 be laid between the belt
layers 15a and 15b as shown in FIG. 2 or on the outside of the belt
layers 15a and 15b as shown in FIG. 1, even though they may be laid
on the inside of the belt layer 15a as shown in FIG. 3. Further,
belt edge cover layers each containing a plurality of organic fiber
cords in a state arranged in a tire circumferential direction may
be laid in the tire widthwise end portions of the belt layers 15a
and 15b in addition to the above compound sheets 16.
[0067] The ratio of the tire circumferential modulus (b) of the
compound sheets 16 to the tire radial modulus (a) thereof (i.e.,
b/a ratio) is adjusted to 1.2 or above by incorporating a short
fiber (A') formed by the fibrillation of a short fiber (A) whose
cross section takes a sea-island structure essentially composed of
at least two polymers and, if necessary a short fiber (B) made of a
thermoplastic polymer having amido groups in the main chain into
the rubber constituting the compound sheets 16 and orienting the
fibrillated short fiber (A') or the hybridized short fibers (A')
and (B) in a tire circumferential direction.
[0068] The tire circumferential rigidity can be enhanced
selectively by laying such anisotropic compound sheets 16 in both
end portions of the belt layers 15a and 15b. Further, road noise
can be reduced with the basic performance parameters such as
comfortableness in riding and stability in steering being kept at
high levels. It is necessary that the ratio of the tire
circumferential modulus (b) of the compound sheets 16 to the tire
radial modulus (a) thereof (i.e., b/a ratio) is adjusted to 1.2 or
above, preferably 1.5 or above. When the ratio is less than 1.2, it
will be difficult to reconcile maintaining the basic tire
performance with the reduction in road noise. Further, the b/a
ratio depends also on hardness of the rubber, loadings of the short
fiber, extrusion process of the sheets and so on. The upper limit
thereof is about 10.
[0069] It is preferable that the compound sheets have a width of at
least 5% of the maximum belt width. When the width of the compound
sheets 16 is less than 5% of the maximum belt width, the
reinforcing effect will be too poor to reduce road noise. When the
width of the compound sheets is too large, the comfortableness in
riding will be poor, even though a high reinforcing effect is
attained. Accordingly, it is preferable that the upper limit of the
width of the compound sheets be 40% of the maximum belt width.
[0070] Next, it is preferable that the compound sheets 16 have a
thickness of 0.3 mm or above. When the thickness of the compound
sheets 16 is less than 0.3 mm, the reinforcing effect will be too
poor to reduce road noise. On the contrary, when the thickness is
too large, the resulting tire will be increased in weight and heat
build-up to result in poor durability, even though a high
reinforcing effect is attained. Accordingly, it is preferable that
the upper limit of the thickness be 3 mm.
[0071] When the fibrillated short fiber (A') is used alone for the
compound sheets 16, the short fiber (A') is incorporated into the
rubber constituting the compound sheets 16 in an amount of 0.5 to
15 parts by weight per 100 parts by weight of the rubber. When the
amount of the fibrillated short fiber (A') is less than 0.5 part by
weight, it will be difficult to adjust the ratio of the tire
circumferential modulus (b) of the compound sheets 16 to the tire
radial modulus (a) thereof (i.e., b/a ratio) to 1.2 or above. When
the amount exceeds 15 parts by weight, the resulting rubber
composition will be very poor in processability in kneading and
extrusion. It is to be noted that the amount of the short fiber
(A') added is substantially equal to the amount of the fibrillated
short fiber (A') incorporated.
[0072] For hybridizing the fibrillated short fiber (A') with the
short fiber (B) the amount the fibrillated short fiber (A')
incorporated is adjusted to 0.5 to 10 parts by weight per 100 parts
by weight of the rubber, while that of the short fiber (B)
incorporated is adjusted to 1 to 15 parts by weight. When the total
amount of the short fibers (A') and (B) incorporated is less than
1.5 parts by weight, it will be difficult to adjust the ratio of
the tire circumferential modulus (b) of the compound sheets 16 to
the tire radial modulus (a) thereof (i.e., b/a ratio) to 1.2 or
above. When the total amount exceeds 25 parts by weight, the
resulting rubber composition will be very poor in processability in
kneading and extrusion.
[0073] FIG. 4 shows an example of the pneumatic radial tire
according to the second embodiment of the present invention. In
FIG. 4, a carcass layer 22 containing a plurality of reinforcement
cords in a state arranged in the radial direction bridges a pair
of, i.e., lefthand and righthand bead portions 21, 21, and the tire
widthwise end portions of the carcass layer 22 are wound up around
the bead cores 23 respectively from the tire inner side to the tire
outer side. Further, a plurality of belt layers 25 each containing
a plurality of steel cords in a state arranged obliquely to the
tire circumferential direction are laid between the tread 24 and
the carcass layer 22 in such a way that the reinforcements cords
contained in one of the belt layers 25 cross those contained in
other layer. The tread 24 has grooves including main grooves 26
extended in the tire circumferential direction, and the groove area
ratio of the tread 24 is adjusted to 30 to 40%.
[0074] The ratio of the tire circumferential modulus (b) of the
tread 24 to the tire radial modulus (a) thereof (i.e., b/a ratio)
is adjusted to 1.2 or above by incorporating a short fiber (A')
formed by the fibrillation of a short fiber (A) whose cross section
takes a sea-island structure essentially composed of at least two
polymers and, if necessary, a short fiber (B) made of a
thermoplastic polymer having amido groups in the main chain into
the rubber constituting the tread 24 and orienting the fibrillated
short fiber (A') or the hybridized short fibers (A') and (B) in a
tire circumferential direction.
[0075] In this embodiment, as described above, the groove area
ratio of the tread 24 is adjusted to 30 to 40% and the tire
circumferential rigidity of the tread is enhanced by imparting
anisotropy to the rubber constituting the tread, by which braking
performance on a dry road surface can be reconciled with that on a
wet road surface at high levels. When the groove area ratio of the
tread 24 is less than 30 % the resulting tire will be poor in
braking performance on a wet road surface. When it exceeds 40 % the
tire will be poor in braking performance on a dry road surface.
[0076] It is necessary that the ratio of the tire circumferential
modulus (b) of the tread 24 to the tire radial modulus (a) thereof
(i.e., b/a ratio) is adjusted to 1.2 or above, preferably 1.5 or
above. When the ratio is less than 1.2, it will be difficult to
reconcile braking performance on a dry road surface with that on a
wet road surface at high levels. Further, the b/a ratio depends
also on hardness of the tread rubber, loadings of the short fiber,
extrusion process of the tread and so on. The upper limit thereof
is about 10.
[0077] When the fibrillated short fiber (A') is used alone for
tread rubber, the short fiber (A') is incorporated into the tread
rubber in an amount of 0.5 to 15 parts by weight per 100 parts by
weight of the rubber. When the amount of the fibrillated short
fiber (A') is less than 0.5 part by weight, it will be difficult to
adjust the ratio of the tire circumferential modulus (b) of the
tread 24 to the tire radial modulus (a) thereof (i.e., b/a ratio)
to 1.2 or above. When the amount exceeds 15 parts by weight, the
resulting rubber composition will be very poor in processability in
kneading and extrusion. It is to be noted that the amount of the
short fiber (A) added is substantially equal to the amount of the
fibrillated short fiber (A') incorporated.
[0078] For hybridizing the fibrillated short fiber (A') with the
short fiber (B), the amount of the fibrillated short fiber (A')
incorporated is adjusted to 0.5 to 10 parts by weight per 100 part
by weight of the rubber, while that of the short fiber (B)
incorporated is adjusted to 1 to 15 parts by weight. When the total
amount of the short fibers (A') and (B) incorporated is less than
1.5 parts by weight, it will be difficult to adjust the ratio of
the tire circumferential modulus (b) of the tread 24 to the tire
radial modulus (a) thereof (i.e., b/a ratio) to 1.2 or above. When
the total amount exceeds 25 parts by weight, the resulting rubber
composition will be very poor in processability in kneading and
extrusion.
[0079] FIG. 5 shows an example of the pneumatic tire according to
the third embodiment of the present invention. In FIG. 3, a carcass
layer 32 containing a plurality of reinforcement cords in a state
arranged in the radial direction bridges a pair of, i.e., lefthand
and righthand bead portions 31, 31, and both tire widthwise end
portions of the carcass layer 32 are wound up around the bead cores
33 respectively from the tire inner side to the tire outer side.
Two belt layers 35, 35 each containing a plurality of reinforcement
cords are laid in the tread portion 34 on the outside of the
carcass layer 32. These belt layers 35, 35 are arranged in such a
way that the reinforcement cords are arranged obliquely to the tire
circumferential direction and that the reinforcement cords
contained in one of the layers 35, 35 cross those contained in the
other layer.
[0080] The tread portion 34 takes a laminate structure constituted
of at least two layers comprising a cap tread 34a lying on the tire
outer side and an under tread 34b lying on the tire inner side, the
cap tread 34a being made of a rubber excellent in wet performance
and the under tread 34b being made of a rubber exhibiting a low
energy loss for the purpose of lowering the rolling resistance. The
energy: loss of the under tread 34b can be reduced by decreasing,
the loadings of carbon black or by using a rubber composition
excellent in impact resilience.
[0081] The ratio of the tire circumferential modulus (b) of the
under tread 34b to the tire widthwise modulus (a) thereof (i.e.,
b/a ratio) is adjusted to 1.5 or above by incorporating a short
fiber (A') formed by the fibrillation of a short fiber (A) whose
cross section takes a sea-island structure essentially composed of
at least two polymers and, if necessary, a short fiber (B) made of
a thermoplastic polymer having amido groups in the main chain into
the rubber constituting the under tread 34b and orienting the
fibrillated short fiber (A') or the hybridized short fibers (A')
and (B) in a tire circumferential direction.
[0082] The incorporation of a short fiber (A') formed by the
fibrillation of a short fiber (A) whose cross section takes a
sea-island structure essentially composed of at least two polymers
into the rubber constituting the under tread 34b in a specific
amount makes it possible to inhibit rubber flow during the molding
of the tire with vulcanization to give an improvement in the
uniformity of the gauge, even when the under tread 34b is made by
using a rubber exhibiting a low energy loss for the purpose of
lowering the rolling resistance of the tire. Further, the resulting
vulcanized tire is improved in stability in steering by virtue of
the high reinforcing effect due to the fibrillated short fiber (A')
oriented in a tire circumferential direction.
[0083] It is necessary that the ratio of the tire circumferential
modulus (b) of the under tread 34b to the tire widthwise modulus
(a) thereof (i.e., b/a ratio) is adjusted to 1.5 or above,
preferably 2.0 or above. When the b/a ratio is less than 1.5, the
hoop effect in the tire circumferential direction will be too poor
to improve the stability in steering.
[0084] Further, the b/a ratio depends also on hardness of the
rubber, loadings of the short fiber, extrusion process of the sheet
and so on. The upper limit thereof is about 10.
[0085] In this embodiment, the under tread rubber exhibits little
rubber flow during the molding of the tire with vulcanization, so
that the thickness of the under tread 34b can be increased as
compared that of the prior art to thereby further lower the rolling
resistance. It is preferable that the volume ratio of the under
tread 34b to the tread portion 34 range from 25 to 40 W. When the
volume ratio is less than 25% the rolling resistance will not
sufficiently be lowered. When it exceeds 40 %, the thickness of the
is cap compound will be smaller than the groove depth of the tread,
so that the under tread will come out to the surface in the last
stage of wear. The term "volume ratio of an under tread" used in
this specification refers to a ratio of the volume of an under
tread to the total volume of a cap tread and an under tread.
[0086] It is also preferable to incorporate carbon black having an
iodine absorption of 30 to 60 mg/g to the rubber constituting the
under tread 34b in an amount of 25 to 60 parts by weight per 100
parts by weight of the rubber. The use of such coarse carbon black
in the above amount can inhibit the rise of tan .delta.. Further,
it is also preferable that the Mooney viscosity of the rubber be 80
or below as determined in a state containing the short fiber,
carbon black and other additives. Good processability can be
secured by adjusting the Mooney viscosity to 80 or below.
[0087] When the fibrillated short fiber (A') is used alone for the
rubber constituting the under tread 34b, the short fiber (A') is
incorporated into the rubber in an amount of 1 to 15 parts by
weight per 100 parts by weight of the rubber. When the amount of,
the fibrillated short fiber (A') is less than one part by weight,
it will be difficult to adjust the ratio of the tire
circumferential modulus (b) of the under tread 34b to the tire
radial modulus (a) thereof (i.e., b/a ratio) to 1.5 or above. When
the amount exceeds 15 parts by weight, the resulting rubber
composition will be very poor in processability in kneading and
extrusion. It is to be noted that the amount of the short fiber (A)
gadded is substantially equal to that of the fibrillated shorts
fiber (A') incorporated.
[0088] For hybridizing the fibrillated short fiber (A') with the
short fiber (B), the amount of the fibrillated short fiber (A')
incorporated is adjusted to 1 to 12 parts by weight per 100 parts
by weight of the rubber, while that of the short fiber (B)
incorporated is adjusted to 1 to 10 parts by weight. When the total
amount of the short fibers (A') and (B) incorporated is less than 2
parts by weight, it will be difficult to adjust the ratio of the
tire circumferential modulus (b) of the under tread 34b to the tire
radial modulus (a) thereof (i.e., b/a ratio) to 1.5 or above. When
the total amount exceeds 22 parts by weight, the resulting rubber
composition will be very poor in processability in kneading and
extrusion.
[0089] FIG. 6 shows an example of the pneumatic tire according to
the fourth embodiment of the present invention. In FIG. 6, a
carcass layer 42 bridges a pair of, i.e., lefthand and righthand
bead portions 41, 41, and both tire widthwise end portions of the
carcass layer 42 are wound up around the bead cores 43 respectively
from the tire inner side to the tire outer side. Further, a
plurality of belt layers 45 each containing a plurality of
reinforcement cords in a state arranged obliquely to the tire
circumferential direction are laid in the tread portion 44 on the
outer peripheral side of the carcass layer 42 in such a way that
the reinforcement cords contained in one of the belt layers 45
cross those contained in the other layer.
[0090] The sidewall 46 located between the bead portion 41 and the
tread portion 44 is made of a rubber composition containing a short
fiber (A') formed by the fibrillation of a short fiber (A) whose
cross section takes a sea-island structure essentially composed of
at least two polymers and, if necessary, a short fiber (B) made of
a thermoplastic polymer having amido groups in the main chain, with
the fibrillated short fiber (A') or the hybridized short fibers
(A') and (B) being oriented in a direction parallel to the face of
the sidewall 46.
[0091] The above incorporation into the rubber constituting the
sidewall 46 of a short fiber (A') formed by the fibrillation of a
short fiber (A) whose cross section takes a sea-island structure
essentially composed of at least two polymers and, if necessary, a
short fiber (B) made of a thermoplastic polymer having amido groups
in the main chain can effectively reinforce the sidewall 46, which
makes it possible to decrease the gauge of the sidewall 46 thus
giving a lightweight tire.
[0092] A rubber composition reinforced with the above short fiber
may constitute at least a part of the sidewall 46. More
specifically, it is preferable that the rubber composition be laid
in a region spreading between the liners corresponding respectively
to 20% and 80% of the tire sectional height (SH). When the region S
in which the short fiber reinforced rubber composition is laid is
narrower than the above range, it will be difficult to secure
satisfactory resistance to external damage. In order to attain a
sufficient reinforcing effect, it is also preferable that the
thickness of the layer made of the short fiber reinforced rubber
composition account for at least 40% of the sidewall thickness.
[0093] With respect to the thickness direction of the sidewall 46,
as shown in FIG. 6, the entire sidewall 46 may be made of the short
fiber reinforced rubber composition. Alternatively, as shown in
FIG. 7, the short fiber reinforced rubber composition may be laid
only in the tire outer portion of the sidewall 46, or as shown in
FIG. 8, it may be laid only in the tire inner portion thereof.
[0094] When the fibrillated short fiber (A') is to be used alone
for the sidewall rubber, the short fiber (A') is incorporated into
the rubber in an amount of 0.5 to 0.15 parts by weight per 100
parts by weight of the rubber. When the amount of the fibrillated
short fiber (A') is less than 0.5% part by weight no satisfactory
reinforcing effect will be attained. When the amount exceeds 15
parts by weight, the resulting rubber composition will be very poor
in processability in kneading and extrusion. It is to be noted that
the amount of the short fiber (A) added is substantially equal to
that of the fibrillated short fiber (A') incorporated.
[0095] For hybridizing the fibrillated short fiber (A') with the
short fiber (B), the amount of the fibrillated short fiber (A')
incorporated is adjusted to 0.5 to 10 parts by weight per 100 parts
by weight of the rubber, while that of the short fiber (B)
incorporated is adjusted to 1 to 15 parts by weight. When the
amount of the short fiber (B) incorporated is less than one part by
weight, the resistance to crack growth will not sufficiently be
improved. When the amount of the fibrillated short fiber (A')
exceeds 10 parts by weight and the amount of the short fiber (B)
exceeds 15 parts by weight, the resulting rubber composition will
be very poor in processability in kneading and extrusion.
[0096] FIG. 9 shows an example of the bead portion of the
heavy-duty pneumatic radial tire according to the fifth embodiment
of the present invention, and FIG. 10 shows the wound-up portion of
the carcass layer. In FIGS. 9 and 10, a carcass layer 52 containing
a plurality of reinforcement cords in a state arranged in the tire
radial direction bridges a pair of, i.e., lefthand and righthand
bead portions 51, 51, and the tire widthwise end portions of the
carcass layer 52 are wound up around the bead cores 53 respectively
from the tire inner side to the tire outer side. Further, bead
fillers 54 made of a hard rubber are laid on the radial outer sides
of the bead cores 53, and enveloped in the wound-up portions of the
carcass layer 52 respectively.
[0097] In the bead portion 51, a steel cord reinforced layer 55
containing a plurality of steel cords in a state arranged in the
tire radial direction is laid along the carcass layer 52, and the
tire outer upper end portion of the steel cord reinforced layer 55
is terminated in the neighborhood of the wound-up portion of the
carcass layer 52. Further, a short fiber reinforced layer 56 is
laid in the wound-up portion of the carcass layer 52 and the upper
end portion of the steel cord reinforced layer 55 as the edge cover
covering both of the portions. Further, an organic fiber cord
reinforced layer 57 containing a plurality of organic fiber cords
(such as nylon cords) in a state arranged obliquely to the tire
circumferential direction is also laid on the tire outer sides of
the wound-up portion of the carcass layer 52 and the upper end
portion of the steel cord reinforced layer 55.
[0098] The ratio of the tire circumferential modulus (b) of the
short fiber reinforced layer 56 to the tire radial modulus (a)
thereof (i.e., b/a ratio) is fiber (A') formed by the fibrillation
of a short fiber (A) whose cross section takes a sea-island
structure essentially composed of at least two polymers and, if
necessary, a short fiber (B) made of a thermoplastic polymer having
amido groups in the main chain into the rubber constituting the
short fiber reinforced layer 56 and orienting the fibrillated short
fiber (A') or the hybridized short fibers (A') and (B) in a tire
circumferential direction.
[0099] The above anisotropic short fiber reinforced layer 56 lying
over the wound-up portion of the carcass layer 52 and the upper end
portion of the steel cord reinforced layer 55 can effectively
inhibit the tire circumferential movement of the cords arranged in
the tire radial direction, so that the stress concentration in the
wound-up end portion of the carcass layer 52 and the upper end
portion of the steel cord reinforced layer 55 can be relaxed with a
decrease in the rubber volume of the bead portion 51. Thus, the
anisotropic short fiber reinforced layer 56 can inhibit the
delamination among cords to thereby improve the durability of the
tire.
[0100] FIG. 11 shows a modification example of the bead portion of
the heavy-duty pneumatic radial tire according to the fifth
embodiment of the present invention. In this embodiment, the same
members as reference numerals as those used in FIG. 9 respectively,
and a detailed description thereof is omitted. In FIG. 11, a short
fiber reinforced layer 56 is laid in the wound-up end portion of
the carcass layer 52. This short fiber reinforced layer 56 is
located between the bead filler 54 and the organic fiber cord
reinforced layer 57, and laid over the region spreading toward the
tire radial outside in a tire radial width of 60 mm from the upper
end portion of the steel cord reinforced layer 55 as a
reinforcement for the bead portion 51.
[0101] The above anisotropic short fiber reinforced layer 56 lying
over the region spreading toward the tire radial outside from the
neighborhood of the wound-up end portion of the carcass layer 52 as
well as that used in the embodiment shown in FIG. 9 not only
improves the durability of the tire but also makes it possible to
secure excellent stability in steering with a decrease in the
rubber volume of the bead portion 51.
[0102] Although the short fiber reinforced layer 56 is required to
lie at least in the neighborhood of the wound-up end of the carcass
layer 52, the form of arrangement thereof is not particularly
limited. Specifically the layer 56 may be used as an edge cover or
as reinforcement for securing the stability in steering.
[0103] It is necessary that the ratio of the tire circumferential
modulus (b) of the short fiber reinforced layer 56 to the tire
radial modulus (a) thereof (i.e., b/a ratio) is adjusted to 1.2 or
above, preferably 1.5 or above. When the ratio is less than 1.2, it
will be difficult to attain an efficacious reinforcing effect.
Further, the b/a ratio depends also on hardness of the rubber,
loadings of the short fiber; extrusion process; of the short fiber
reinforced layer 56 and so on. The upper limit thereof is about
10.
[0104] When the fibrillated short fiber (A') is to be used alone
for the rubber constituting the short fiber reinforced layer 56,
the short fiber (A') is incorporated into the rubber in an amount
of 0.5 to 15 parts by weight per 100 parts by weight of the rubber.
When the amount of the fibrillated short fiber (A') is less than
0.5 part by weight, it will be difficult to adjust the ratio of the
tire circumferential modulus (b) of the short fiber reinforced
layer 56 to the tire radial modulus (a) thereof (i.e., b/a ratio)
to 1.2 or above. When the amount exceeds 15 parts by weight, the
resulting rubber composition will be very poor in processability in
kneading and extrusion. It is to be noted that the amount of the
short fiber (A) added is substantially equal to that of the,
fibrillated short fiber (A') incorporated.
[0105] For hybridizing the fibrillated short fiber (A') with the
short fiber (B), the amount of the fibrillated short fiber (A')
incorporated is adjusted to 0.5 to 10 parts by weight per 100 parts
by weight of the rubber, while that of the short fiber (B)
incorporated is adjusted to 1 to 15 parts by weight. When the total
amount of the fibrillated short fiber (A') and short fiber (B)
incorporated is less than a 1.5 parts by weight, it will be
difficult to adjust the ratio of the tire circumferential modulus
(b) of the short fiber reinforced layer 56 to that tire radial
modulus (a) thereof (i.e., b/a ratio) to 1.2 or above. When the
total amount exceeds 25 parts by weight, the resulting rubber
composition will be very poor in processability in kneading and
extrusion.
[0106] FIG. 12 shows an example of the pneumatic radial tire
according to the sixth embodiment of the present invention. In FIG.
12, a carcass layer 62 containing a plurality of reinforcement
cords in a state arranged in the radial direction briges a pair of,
i.e., lefthand and righthand bead portions 61, 61, and the tire
widthwise end portions of the carcass layer 62 are wound up around
the bead cores 63 respectively from the tire inner side to the tire
outer side. A bead filler 64 is located on the outer peripheral
side of the bead core 63, and enveloped in the wound-up portion of
the carcass layer 62. Further, two belt layers 66, 66 each
containing a plurality of steel cords are laid in the tread portion
0.65 on the outside of the carcass layer 62. These belt layers
66,66 are arranged in such a way that the reinforcement cords are
arranged obliquely to the tire circumferential direction and that
the reinforcement cords contained in one of the layers 66, 66 cross
those contained in the other layer.
[0107] The rubber constituting the bead filler 64 contains a short
fiber (A'), formed by the fibrillation of a short fiber (A) whose
cross sections takes a sea-island structure essentially composed of
at least two polymers and, if necessary, a short fiber (B) made of
a thermoplastic polymer having amido groups in the main chain, with
the fibrillated short fiber (A') or the hybridized short fibers
(A') and (B) being oriented in a direction perpendicular to the
tire radial direction, by which the ratio of the storage modulus
(b) of the bead filler 64 in the direction of orientation of the
short fiber to the tire radial storage modulus (a) thereof (i.e.,
b/a ratio) is adjusted to 4 to 10.
[0108] The short fiber contained in the bead filler 64 may be
oriented in the tire cicumferential direction as shown in FIG. 13,
or in the tire rotating shaft direction as shown in FIG. 14.
Alternatively, the bead filler 64 may take a structure constituted
of two layers laminated in the tire rotating shaft direction as
shown in FIG. 15, one (64a) of the layers containing the short
fiber in a state oriented in the tire circumferential direction and
the other (64b) containing it in a state, oriented in the tire
rotating shaft direction. The use of the two-layer bead filler 64
shown in FIG. 15 enables such a design that both the rigidity of
the bead portion 61 in the tire circumferential direction and that
in the tire rotating shaft direction fall in their respective
suitable ranges
[0109] The anisotropic bead filler 64 located on the outer
peripheral side of the bead core 63 can selectively enhance the
rigidity in the tire circumferential or tire axial direction, which
brings about an improvement in the comfortableness in riding and a
decrease in the tire weight with the stability in steering being
kept at a level equivalent or superior to that of a tire provided
with steel reinforcements in the neighborhood of the bead fillers.
It is necessary that the ratio of the storage modulus (b) of the
bead filler 64 in the direction of orientation of the short fiber
to the tire radial storage modulus (a) thereof (i.e., b/a ratio) is
adjusted to 4 or above, preferably 6 or above. When the b/a ratio
is less than 4, it is difficult to reconcile stability in steering
with comfortableness in riding. The b/a ratio depends also on
hardness of the rubber, loadings of the short fiber, extrusion
process of the sheet or the like. The upper limit thereof is
10.
[0110] When the fibrillated short fiber (A') is to be used alone
for the rubber constituting the bead filler 64, the amount of the
short fiber (A') incorporated is adjusted to 3 to 15 parts by
weight, weight of the rubber. When the amount is less than 3 parts
by weight, it will be difficult to adjust the ratio of the storage
modulus (b) of the bead filler 64 in the direction of orientation
of the short fiber to the tire radial storage modulus (a) thereof
(i.e., b/a ratio) to 4 or above. When the amount exceeds 15 parts
by weight, the resulting rubber compositions will be very poor in
processability in kneading and extrusion. It is to be noted that
the amount of the short fiber (A) added is substantially equal to
that of the fibrillated short fiber (A') incorporated.
[0111] For hybridizing the fibrillated short fiber (A') with the
short fiber (B), the amount of the fibrillated short fiber (A')
incorporated is adjusted to 3 to 10 parts by weight per 100 parts
by weight of the rubber, while that of the short fiber (B)
incorporated is adjusted to 1 to 15 parts by weight. When the total
amount of the short fibers (A') and (B) incorporated is less than 4
parts by weight, it will be difficult to adjust the ratio of the
storage modulus (b) of the bead filler 64 in the direction of
orientation of the short fiber to the tire radial storage modulus
(a) thereof (i.e., b/a ratio) to 4 or above. When the total amount
exceeds 25 parts by weight, the resulting rubber composition will
be very poor in processability in kneading and extrusion.
[0112] In the present invention, the rubber member into which the
fibrillated short fiber (A') is incorporated is made from at least
one rubber. Although this rubber is not particularly limited,
examples of the rubber include: diene rubbers and hydrogenated
derivatives thereof such as natural rubbers (NR), polyisoprene
rubbers (IR), epoxidized natural rubbers (ENR), styrene/butadiene
copolymer rubbers (SBR), poly-butadiene rubbers (high-cis BR and
low-cis BR), nitrile rubbers (NBR), hydrogenated NBR and,
hydrogenated SBR; and various elastomers such as olefin rubbers,
example, ethylene/propylene rubbers (EPDM and EPM), maleic
acid-modified ethylene/propylene rubbers (M-EPM), butyl rubbers
(IIR) and isobutylene/(aromatic vinyl or diene) copolymers,
halogenated rubbers, for example, brominated butyl rubbers
(Er-IIR), chlorinated butyl rubbers (Cl-IIR), brominated
isobutylene/p-methylstyrene copolymers (Br-IPMS), chlorosulfonated
polyethylene (CMS), chlorinated polyethylene (CM) and maleic
acid-modified chlorinated polyethylene (M-CM), and thermoplastic
elastomers, for example, styrene elastomers, olefin elastomers and
ester elastomers.
[0113] Also it is necessary that the short fiber (A) is essentially
composed of at least two polymers which are not compatible with
each other but form a sea-island structure in the cross section
thereof and has such fibrillability that the sea component and the
island component can be separated from each other by mechanical
shear force to give finer fibers, even though the polymers
constituting the short fiber (A) constituting the short fiber (A)
include polyester, polyvinyl alcohol, nylon, polyethylene,
polypropylene, cellulose, polybutadiene, aromatic polyamide, rayon,
polyarylate, poly(p-phenylenebenzobisoxazole)
poly(p-phenylene-benzobisthiazole) and so on.
[0114] The addition of the above fibrillable short fiber. (A) to
the rubber exhibits only a little "intertwist" of the fiber by
virtue of the low aspect ratio of the fiber (the term "aspect
ratio" being a ratio of fiber length to the diameter of a circle
having an area equivalent to the sectional area of the fiber), so
that the fiber can be well dispersed in the rubber. Then, the short
fiber (A) is fibrillated by separating the sea component from the
island component by mechanical shear force, and the short fiber
(A') formed by the fibrillation has an increased area of contact
with the rubber to exhibit a high rubber reinforcing effect. The
fibrillation of the short fiber (A) may be conducted by division
(diameter reduction) over the whole section or by diameter
reduction only in the periphery or both end portions of the fiber
with the core remaining unfibrillated.
[0115] It is preferable that the short fiber (A) have an average
length of 1 to 5000 .mu.m. When the average length of the short
fiber (A) is less than 1 .mu.m, the resulting rubber will not
exhibit satisfactory rubber composition will be very poor in
processability in kneading and extrusion. Further, it is preferable
that the fibrillated short fiber (A') have an average diameter of
0.05 to 5.0 .mu.m, still preferably 0.1 to 2 .mu.m. When the
average diameter of the fibrillated short fiber (A') is less than
0.05 .mu.m, not only a prolonged kneading time will be necessary,
but also fibrillation into such too fine fibers will not give any
additional reinforcing effect. On the contrary, when the average
diameter exceeds 5.0 .mu.m, the resulting fiber will not exhibit
satisfactory affinity for the rubber owing to the insufficient
fibrillation, so that the resulting rubber composition will be
liable to cause cracking.
[0116] A preferable example of the short fiber (A) to be used in
the present invention is a short fiber at least comprising a
polyvinyl alcohol polymer (X) and a water-insoluble polymer (Y) at
an X/Y weight ratio of 90/10 to 20/80 and having a sea-island
structure wherein one of X and Y is present as the island component
and the other thereof is present as the sea component. In this
short fiber, a sea-island structure is formed by a combination of a
polyvinyl alcohol polymer (X), which is a water-soluble polymer
with a water-insoluble polymer (Y) (such as cellulose acetate or
starch) which is not dissolved in water even when immersed in water
at ordinary temperature. A polyvinyl alcohol polymer exhibits high
strength and excellent affinity for rubbers. When the content of
the polyvinyl alcohol polymer (X) in the short fiber exceeds 90% by
weight, the resulting short fiber will not be divided by mechanical
shear force applied during the kneading of the rubber composition.
When it is less than 20% by weight not reinforcing effect will be
attained.
[0117] Alternatively, an acrylonitrile polymer may be used as the
water-insoluble polymer (Y) together with the above
polyvinyl-alcohol polymer (X). Such a combination of a polyvinyl
alcohol polymer with an acrylonitrile polymer is desirable in
respects of the division (diameter reduction) of the fiber and
strength. The production of a polyvinyl alcohol fiber is conducted
by solvent spinning which is a representative wet spinning process,
and dimethyl sulfoxide (DMSO) is sometimes used as the solvent for
a dope. In such a case, the combination of a polyvinyl alcohol
polymer with an acrylonitrile polymer is preferable from the
standpoint of easiness in preparation, because an acrylonitrile
polymer is also soluble in DMSO.
[0118] The above polyvinyl alcohol polymer (X) may be any of
completely and partially saponified ones and copolymers. The
acrylonitrile polymer to be used in the present invention may be
any one containing at least 70 mole % of acrylonitrile. For
example, the acrylonitrile polymer may be one prepared by
copolymerizing acrylonitrile with a (meth)acrylate ester such as
methyl acrylate, ethyl acrylate or methyl methacrylate, a vinyl
ester such as vinyl acetate or vinyl butyrate, a vinyl compound
such as vinyl chloride, an unsaturated carboxylic acid such as
acrylic acid, methacrylic acid or maleic anhydride, a sulfonated
vinyl compound, a monomer covulcanizable with rubbers (such as
butadiene or isoprene) or the like. Further, it is preferable in
order to enhance the solubility in the solvent of a dope that the
acrylonitrile polymer to be used in the present invention be not
PAN homopolymer but acrylonitrile copolymers containing other
comonomer in an amount of 0.5 to 10 mole %, still preferably 2 to 8
mole %.
[0119] Prior to the addition of the short fiber (A) to the rubber,
the short fiber (A) may be surface-treated by dipping into a rubber
latex, a liquid rubber, a liquid resin, a water-soluble resin, a
thermoplastic resin or the like, for the purpose of enhancing the
binding between the fibers to thereby accelerate the dispersion
thereof in the rubber. Further, bonding compounds such as phenolic
compounds and methylene donors may be added to the rubber in order
to improve the bonding between the short fiber (A) and the rubber
through vulcanization.
[0120] Examples of the phenolic compounds include resorcinol,
.beta.-naphthol and resorcinol/aldehyde condensates (resorcin
resins), m-cresol/aldehyde condensates (m-cresol resins),
phenol/aldehyde other phenolic organic compounds with aldehydes.
Examples of the methylene donors include hexamethylenetetramine,
hexamethoxymethylolmelamine, paraformaldehyde,
acetaldehyde/ammonia, .alpha.-polyoxy-methylene,
polymethylolacetyleneurea, and derivatives thereof.
[0121] The fibrillated short fiber (A') is excellent in affinity
for rubbers, so that no problem occurs even when these additives
are not used. When the above phenolic compound and methylene donor
are used, it is preferable that the amount of the former be
adjusted to 10 parts by weight or below, still preferably 6 parts
by weight or below per 100 parts by weight of the rubber, while
that of the latter be adjusted to 10 parts by weight or below,
still preferably 5 parts by weight or below per 100 parts by weight
thereof.
[0122] When the amounts exceed the upper limits respectively,
unfavorably the resulting rubber composition will be poor in
processability and in elongation at break. In addition to these
additives, other bonding compounds may be added, and such bonding
compounds include silane coupling agents, titanate coupling agents,
unsaturated carboxylic acids and derivatives thereof, epoxy resins,
epoxidized liquid oligomers and polymers, maleic anhydride-modified
liquid oligomers and polymers, and blocked isocyanlates.
[0123] The above fibrillated short fiber (A') can remarkably
enhance the modulus at low elongation, but it little enhances the
modulus at high elongation. It is therefore preferable to add a
short fiber (B) made of a thermoplastic polymer having amido groups
in the main chain in addition to the above fibrillated short fiber
(A'). This short fiber (B) can remarkably enhance the modulus at
high elongation, so that the hybridization of the fibrillated short
fiber (A') with the short fiber (B) makes it possible to enhance
both the modulus at low elongation and that at high elongation
simultaneously. Enhancement in the modulus at high elongation makes
it possible to inhibit the initiation and growth of cracks due to
flex fatigue, thus bringing about an improvement in the resistance
to crack growth.
[0124] The above short fiber (B) is made of a thermoplastic polymer
having amido groups in the main chain. It is preferable that the
average diameter of the short fiber (B) lie within the range of
0.05 to 5.0 .mu.m. The short fiber (B) is incorporated into the
rubber by preparing a composition which comprises the short fiber
(B) and a matrix made of a rubber and/or a polyolefin and wherein
the short fiber (B) is dispersed in the matrix and chemically
bonded to the matrix and adding this composition to the rubber.
Examples of such a composition containing the short fiber (B)
include the following items (i),(ii) and
[0125] (i) Reinforced rubber compositions each comprising 100 parts
by weight of a vulcanizable rubber and 1 to 100 parts by weight of
a fine short fiber made of a thermoplastic polymer having amido
groups in the molecule, wherein the fine short fiber is embedded in
the rubber and the polymer is grafted onto the vulcanizable rubber
at the interface of the fiber through a novolak base
phenol/formaldehyde precondensate (see Japanese Patent Laid-open
No. 43041/1984).
[0126] Examples of the novolak-base phenol/formaldehyde
precondensate include soluble and fusible-resins obtained by
condensing a phenol such as phenol or bisphenol with formaldehyde
(or paraformaldehyde) in the presence of an acid catalyst such as
sulfuric acid, hydrochloric acid, phosphoric acid or oxalic acid
and modifications thereof.
[0127] (ii) Fiber-reinforced thermoplastic compositions each
comprising a matrix made of a polyolefin and an elastomer and a
thermoplastic polyamide dispersed in the matrix in the form of a
fine fiber chemically bonded to the matrix through a silane
coupling agent (see Japanese Patent Laid-open No. 278360/1995).
[0128] Examples of such a silane coupling agent include
vinylalkoxysilanes, such as vinyltrimethoxysilane,
vinyltriethoxysilane and vinyltris (.beta.-methoxyethoxy) silane,
vinyltriacetylsilane, .gamma.-methacryloxypropyl-trimethoxysilane,
.gamma.-[N-(.beta.-methacryl-
oxyethyl)-N,N-dimethylammonium(chloride)-]propylmethoxysilane,
N-.beta.-(aminoethyl)-.gamma.-aminopropyltrimethoxysilane,
styryl-diaminosilane, and .gamma.-ureidopropyltriethoxysilane.
[0129] (iii) Reinforced rubber compositions each comprising 100
parts by weight of a vulcanizable rubber and 1 to 70 parts by
weight of a fine nylon fiber having an average diameter of 0.05 to
0.8 .mu.m, wherein the fine fiber is embedded in the vulcanizable
rubber and the nylon is grafted onto the vulcanizable rubber at the
interface of the fiber through a resol-base
alkylphenol/formaldehyde precondensate (see Japanese Patent
Laid-open No. 79037/1983).
[0130] Examples of the resol-base alkylphenol/formaldehyde
precondensate include those obtained by reacting an alkylphenol
such as cresol with formaldehyde or acetaldehyde in the presence of
an alkali catalyst and modifications thereof. In particular, it is
favorable to use a resol-base alkylphenol/formaldehyde
precondensate having two or more methylol groups in the
molecule.
[0131] The vulcanizable rubbers constituting the compositions
described in the items (i) and (iii) and the elastomer constituting
the compositions described in the item (ii) are the same as those
constituting the rubber member into which the fibrillated short
fiber (A') is incorporated. Further, thermoplastic polyamides and
urea resins are, usable as the thermoplastic-polymer-having amido
groups and constituting the compositions described in the item (i)
and the thermoplastic polyamide constituting the compositions
described in the item (ii). In particular, it is preferable to use
one having a melting point of 135 to 350.degree. C. Thermoplastic
polyamides having melting points of 150 to 300.degree. C. are
particularly preferable.
[0132] Examples of the thermoplastic polyamide include nylon 6,
nylon 66, nylon 6/nylon 66 copolymers, nylon 610, nylon 612, nylon
46, nylon 11, nylon 12, nylon MXD 6, xylylenediamine/adipic acid
polycondensates, xylylenediamine/pimelic acid polycondensates,
xylylenediamine/suberic acid polycondensates,
xylylenediamine/azelaic acid polycondensates,
xylylenediamine/sebacic acid polycondensates,
tetramethylenediamine/terep- hthalic acid polycondensates,
hexamethylenediamine/terephthalic acid polycondensates,
octamethylenediamine/terephthalic acid polycondensates,
trimethylhexamethylenediamine/terephthalic acid polycondensates,
decamethylenediamine/terephthalic acid polycondensates,
undecamethylenediamine/terephthalic acid polycondensates,
dodecamethylenediamine/terephthalic acid polycondensates,
tetramethylenediamine/isophthalic acid polycondensates,
hexamethylenediamine/isophthalic acid polycondensates,
octamethylenediamine/isophthalic acid polycondensates,
trimethylhexamethylenediamine/isophthalic acid polycondensates,
decamethylenediamine/isophthalic-acid polycondensates,
undecamethylenediamine/isophthalic acid polycondensates and
dodecamethylenediamine/isophthalic acid polycondensates.
[0133] Among these thermoplastic polyamides, those having melting
points of 160 to 265.degree. C. are particularly preferable.
Specific examples of such thermoplastic polyamides include nylon 6,
nylon 66, nylon 6/nylon 66 copolymers, nylon 610, nylon 612, nylon
46, nylon 11 and nylon 12.
[0134] The polyolefin constituting the compositions described in
the item (ii) is one having a melting point of 80 to 250.degree. C.
Alternatively, polyolefins having softening points of 50.degree. C.
or above, particularly 50 to-200.degree. C. are also favorably
usable. Preferable examples of such polyolefins include homo- and
co-polymers of C.sub.2-C.sub.8 olefins, copolymers of
C.sub.2-C.sub.8 olefins with aromatic vinyls such as styrene,
chlorostyrene and .alpha.-methylstyrene, copolymers of C.sub.2-C8
olefin with vinyl acetate, copolymers of C.sub.2-C.sub.8 olefins
with acrylic acid or esters thereof, copolymers of C.sub.2-C.sub.8
olefins with methacrylic acid or esters thereof, and copolymers of
C.sub.2C.sub.8 olefins with vinylsilanes.
[0135] Specific examples of the polyolefins include high-density
polyethylene, low-density polyethylene, polypropylene,
ethylene/propylene block copolymers, ethylene/propylene random
copolymers, linear low-density polyethylene, poly-4,
methylpentene-1, poly-butene-1, polyhexene-1, ethylene/vinyl
acetate co-polymers, methylene/acrylic acid copolymers,
ethylene-/methyl-acrylate copolymers, ethylene/ethyl
acrylate-copolymers, ethylene/propyl acrylate copolymers,
ethylene/butyl acrylate copolymers, ethylene/2-ethylhexyl acrylate
copolymers, ethylene/hydroxyethyl acrylate copolymers,
ethylene/vinyltrimethoxysilane copolymers,
ethylene/vinyltriethoxysilane copolymers, ethylene/vinylsilane
copolymers, ethylene/styrene copolymers, and propylene/styrene
copolymers. Further, halogenated polyolefins such as chlorinated
brominated or chlorosulfonated polyethylene are also favorably
usable. These polyolefins may be used each alone or as a mixture of
them.
[0136] Next, description will be made on the molding process for
the rubber member according to the present invention. First, a
predetermined amount of a short fiber (A) whose cross section takes
a sea-island structure essentially composed of at least two
polymers is added to a rubber composition containing carbon black,
a vulcanizing agent, a vulcanization accelerator, a process oil and
so on, followed by, if necessary, the addition of a predetermined,
amount of a composition comprising a short fiber (B) made of a
thermoplastic polymer having amido groups in the main chain and the
matrix wherein the fiber (B) is dispersed in the matrix and
chemically bonded to the matrix. Then, the resulting mixture is
masticated in a Banbury mixer to thereby disperse the short fibers
(A) and (B) in the rubber uniformly.
[0137] The masticated composition is further kneaded between a pair
of open rolls by applying mechanical shear force thereto to thereby
fibrillate the short fiber (A) into the above short fiber (A')
having an average diameter of 0.05 to 5.0 .mu.m. The composition
thus obtained is molded by the use of an extruder or the like into
a sheet to thereby orientate the short fibers (A') and (B) in a
predetermined direction.
EXAMPLE 1
[0138] Invention Tires 101 to 107 and Comparative Tires 101 and 102
each provided with compound sheets in both end portions of the belt
layers respectively were produced, wherein the ratio of the tire
circumferential modulus (b) of the compound sheets to the tire
radial modulus (a) thereof (i.e., b/a ratio) was varied by
incorporating a short fiber (A') formed by the fibrillation of a
short fiber (A) whose cross section took a sea-island structure
essentially composed of polyvinyl alcohol and cellulose acetate,
and if necessary, a composition wherein a short fiber (B) made of
nylon 6 having amido groups in the main chain was dispersed in a
rubber matrix and chemically bonded to the matrix into the rubber
constituting the compound sheets and orienting the fibrillated
short fiber (A') and the short fiber (B) in a tire circumferential
direction. Further, Conventional Tire 101 was also produced, which
was provided with compound sheets not containing any short fiber.
The sizes of these tires were 185/65R14 86H. In producing Invention
Tires 101 to 107 and Comparative Tire 101 and 102, the short fibers
(A) and (B) were used in various amounts per 100 parts by weight of
the rubber. Further, these test tires were made different also in
the ratio (%) of the width of the compound sheets to the maximum
belt width and/or in the thickness (mm) of the compound sheets.
[0139] These test tires were evaluated for road noise and
durability in high-speed running, and the results are given in
Table 1.
[0140] Road Noise:
[0141] These test tires were put on wheels having rim sizes of
14.times.5.multidot.1/2 JJ, and the air pressure was adjusted to
210 kPa. The resulting assemblies were mounted on an automobile
having an engine displacement of 1800 cc. A microphone was set in
the automobile on the window side of the driver's seat at the
position corresponding to the ears of a driver, and the resulting
automobile was made to travel on a rough road surface at a speed of
60 km/h to measure the interior noise. Thus, the sound pressure
(dB) at 315 Hz was determined. The results are given in terms of
differences from the value (reference) observed in the car mounted
with Conventional Tire 101. A negative value means a road noise
level smaller than the reference.
[0142] Durability in High-Speed Running:
[0143] Each test tire was put on a wheel having rim sizes of
14.times.5.multidot.1/2, and the air pressure was adjusted to 210
kPa. The resulting assembly was mounted on a drum tester, and
subjected to the test D4230 to measure the distance covered until
thee belt edge got out of order. The results are given in terms of
indexes as calculated by taking the value of Conventional Tire 101
as 100. A larger index means more excellent durability in
high-speed running.
1TABLE 1 Comp. Comp. Conventional Tire Invention Invention
Invention Invention Invention Invention Invention Tire Tire 101 101
Tire 101 Tire 102 Tire 103 Tire 104 Tire 105 Tire 106 Tire 107 102
b/a 1 1.1 1.3 1.3 1.3 4.8 1.3 1.3 3.1 9.2 Short fiber (A) 0 0.3 0.6
0.6 0.6 4 0.6 0.6 3 17 (pt. wt.) Short fiber (B) 0 0 0 0 0 0 0 0 1
0 (pt. wt.) Width of -- 20 20 20 20 20 7 20 20 20 compound sheet
(no sheet used) (%) Thickness of -- 0.6 0.6 0.6 0.6 0.6 0.6 0.3 0.6
0.6 compound sheet (no sheet used) (mm) Road noise (dB) ref. -0.1
-0.5 -0.8 -0.3 -1.0 -0.3 -0.3 -1.0 -1.0 Durability in 100 100 100
100 100 100 100 100 102 100 high-speed running Processability
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. X Arrangement of -- compound sheets
[0144] As apparent from the results given in Table 1, Invention
Tires 101 to 107 were reduced in road noise with their durability
in high-speed running which is one of the basic tire performance
parameters being kept at high levels. Comparative Tire 101 was
unsatisfactory reduced in road noise owing to poor anisotropy of
the compound sheets. Further, Comparative Tire 102 was reduced in
road noise, but was disadvantageous in that the compound sheets
were very poor in processability because of the presence of the
short fiber in an excess.
EXAMPLE 2
[0145] Invention Tires 201 to 206 were produced, wherein the ratio
of the tire circumferential modulus (b) of the tread to the tire
radial modulus (a) thereof (i.e., b/a ratio) was varied by
incorporating a short fiber (A') formed by the fibrillation of a
short fiber (A) whose cross-section took a sea-island structure
essentially composed of polyvinyl alcohol and cellulose acetate,
and if necessary, a composition wherein a short fiber (B) made of
nylon 6 having amido groups in the main chain was dispersed in a
rubber matrix and chemically bonded to the matrix into the rubber
constituting the tread and orienting the fibrillated short fiber
(A') and the short fiber (B) in a tire circumferential direction.
Further, Conventional Tires 201 and 202 were also produced, the
treads of which did not contain any short fiber. The sizes of these
tires were 185/65R14 86H. In producing Invention Tires 201 to 206,
the short fibers (A) and (B) were used in various amounts per 100
parts by weight of the rubber. Further, the treads of the tires had
a block pattern and their groove area ratios were adjusted to
35%.
[0146] These test tires were evaluated for both braking performance
on a dry road surface and that on a wet road surface by the
following testing methods, and the results are given in Table 2. In
Table 2, the JIS-A hardness-values of the tread rubbers at
20.degree. C. are also given in terms of indexes as calculated by
taking the hardness of Conventional. Tire 201 as 100. Further, the
tans .delta. values of the tread rubbers of the test tires were
adjusted to the same level.
[0147] Braking Performance on Dry Road Surface:
[0148] These test tires were put on wheels having rim sizes of
14.times.51/2, and the air pressure was adjusted to 210 kPa. The
resulting assemblies were mounted on an automobile having an engine
displacement of 1800 cc. The automobile was made to travel on a dry
road surface at a speed of 80 km/h, and then braked to a halt to
measure the braking distance. The results are given in terms of
indexes as calculated by taking the inverse number of the measured
value of Conventional Tire 201 as 100. A larger index means more
excellent braking performance on a dry road surface.
[0149] Braking Performance on a Wet Road Surface:
[0150] Test tires were put on wheels having rim sizes of
14.times.5.multidot.1/2, and the air pressure was adjusted to 210
kPa. The resulting assemblies were mounted on an automobile having
an engine displacement of 1800 cc. The automobile was made to
travel on a wet road surface at a speed of 80 km/h, and then braked
to a halt to measure the braking distance. The results are given in
terms of indexes as calculated by taking the inverse number of the
measured value of Conventional Tire 201 as 100. A larger index
means more excellent braking performance on a wet road surface.
2 TABLE 2 Braking Braking Hardness per- per- of tread Short Short
formance formance rubber b/a fiber A fiber B (dry) (wet)
Conventional 100 1 -- -- 100 100 Tire 201 Conventional 90 1 -- --
97 102 Tire 202 Invention 90 1.2 0.5 -- 108 112 Tire 201 Invention
90 9.7 15 -- 112 113 Tire 202 Invention 90 1.2 0.5 1 110 113 Tire
203 Invention 90 3.0 0.5 15 114 115 Tire 204 Invention 90 8.4 10 1
117 119 Tire 205 Invention 90 9.2 10 15 118 120 Tire 206
[0151] As apparent from the results given in Table 2, Invention
Tires 201 to 206 were able to be improved in both braking
performance on a dry road surface and that on a wet road surface,
as compared with Conventional Tires 201 and 202.
[0152] Table 3 shows results as observed with respect to tires
which had the same tire sizes as described above and whose treads
had a ratio of tire circumferential modulus (b) to tire radial
modulus (a) (i.e., b/a ratio) of 1.2 and various groove area
ratios.
3 TABLE 3 Groove Braking Braking area performance performance b/a
ratio (dry) (wet) Comp. Tire 201 1.2 25 99 101 Invention Tire 207
1.2 30 105 106 Invention Tire 208 1.2 35 104 108 Invention Tire 209
1.2 40 103 105 Comp. Tire 202 1.2 45 97 100
[0153] As apparent from the results given in Table 3, Invention
Tires 207 to 209 were improved in both braking performance on a dry
road surface and that on a wet road surface, which supports the
necessity of limiting the groove area ratio of the tread to 30 to
40%.
EXAMPLE 3
[0154] Invention Tires 301 to 305 each provided with a two-layer
tread constituted of a cap tread and an under tread were produced,
wherein the ratio of the tire circumferential modulus (b) of the
under tread to the tire widthwise modulus (a) thereof (i.e., b/a
ratio) was varied by incorporating a short fiber (A') formed by the
fibrillation of a short fiber (A) whose cross section took a
sea-island structure essentially composed of polyvinyl alcohol and
cellulose acetate, and if necessary, a composition wherein a short
fiber (B) made of nylon 6 having amido groups in the main chain was
dispersed in a rubber matrix and chemically bonded to the matrix
into the rubber constituting the under tread and orienting the
fibrillated short fiber.(A') and the short fiber (B) in a tire
circumferential direction. Further Conventional Tire 301 and
Comparative Tires 301 to 303 whose under treads did not contain any
short fiber and Comparative Tires 304 to 306 whose under treads
contained the short fiber(s) were also produced. The sizes of these
tires were 185/65R14 86H. In producing Invention Tires 301 to 305
and Comparative Tires 304 to 306, the short fibers (A) and (B) were
used in various amounts per 100 parts by weight, of the rubber.
[0155] These test tires were evaluated for rolling resistance,
stability in steering and durability in high-speed running by the
following testing methods, and the results are given in Table 4.
The formulations of the under treads are given more specifically in
Table 5. In Table 4, each figure in parentheses in the row of
"short fiber (B)" refers to the amount of nylon.
[0156] Rolling Resistance:
[0157] Each test tire was put on a wheel having rim sizes of
14.times.5.multidot.1/2 JJ, and the air pressure was adjusted to
210 kPa. The resulting assembly was mounted on a drum tester and
examined for rolling resistance by the use of a load cell. The
results are given in terms of indexes as calculated by taking the
rolling resistance of Conventional Tire 301 as 100. A smaller index
value means lower rolling resistance.
[0158] Stability in Steering:
[0159] Test tires were put on wheels having rim sizes of
14.times.5.multidot.1/2 JJ, and the air pressure was adjusted to
210 kPa. The resulting assemblies were mounted on an automobile
having an engine displacement of 1800 cc, and the resulting
automobile was evaluated for stability in steering by five test
drivers according t a feeling test. The results are given, in five
ranks. A higher value means more excellent stability in
steering.
[0160] Durability in High-Speed Running:
[0161] Each test tire was put on a wheel having rim sizes of
14.times.5.multidot.1/2 JJ, and the air pressure was adjusted to
210 kPa. The resulting assembly was mounted on a drum tester and
subjected to the test of durability in high-speed running according
to JIS D4230. In Table 4, ".circleincircle." refers to excellent,
".largecircle." good, ".DELTA." fair, and "X" bad.
4TABLE 4 Inven- Inven- Inven- Conven- Comp. Comp. Comp. tion tion
Comp. Comp. tion Invention Invention Comp. tional Tire Tire Tire
Tire Tire Tire Tire Tire Tire Tire Tire Formulation of rubber Tire
301 301 302 303 301 302 304 305 303 304 305 306 NR phr 70 70 60 60
60 60 60 60 60 60 60 60 SBR phr 30 30 BR phr 40 40 40 40 40 40 40
40 40 40 Carbon phr 50 40 50 65 50 50 50 50 50 50 50 50 Short
fiber(A) phr 1 5 15 3 12 17 Short fiber(B) phr (Ny) 15 (5) 45 (15)
3 (1) 30 (10) Physical properties JIS hardness 58 53 54 61 61 67 62
76 81 66 85 82 Mooney viscosity 70 60 65 85 65 61 69 87 42 63 78 41
Processability in extrusion .largecircle. .largecircle.
.circleincircle. .circleincircle. .circleincircle. .largecircle.
.largecircle. X .DELTA. .largecircle. .DELTA. X Rubber flow .DELTA.
X X .DELTA. .largecircle. .circleincircle. .largecircle.
.largecircle. .circleincircle. .largecircle. .circleincircle.
.circleincircle. b/a (mm) 1 1 1 1 1.5 3.8 2 3.2 7.1 2.5 5.6 7.3
thickness of under tread 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2
1.2 1.2 Test results Rolling resistance 100 99 98 101 98 98 99 99
98 98 98 98 Stability in steering 3 2 2.5 3.5 3 3.5 2.5 3 4 3 4 4
Durability in high-speed .largecircle. .largecircle. .largecircle.
X .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .circleincircle. .circleincircle. .largecircle.
running
[0162]
5TABLE 5 Formulation of Amt. rubber Trade name Maker (Phr) NR RSS
#3 variable SBR Nipol 1502 Nippon Zeon Co., Ltd. variable BR Nipol
BR1220 Nippon Zeon Co., Ltd. variable short fiber K-II SA Kuraray
Co., Ltd. variable (A) UBE HA1060 Ube Industries, Ltd. variable
short fiber HTC-100 Chubu Carbon 50 (B) Komorex 300 Nippon Oil Co.,
Ltd. 5 carbon (FEF) zinc white #3 Shodo Kagaku 5 aromatic oil Bee's
stearic acid 1 zinc oxide Nocrac 224 Ohuchi Shinko Kagaku 1 stearic
acid Sanshin Chemical Industry 3 age resister Nocceler NS-F Ohuchi
Shinko Kagaku 1 sulfur vulcanization accelerator
[0163] As apparent from the results given in Table 4, the amount of
carbon used for Comparative Tire 301 was smaller than that used for
Conventional Tire 301, so that Comparative Tire 301 was poorer in
stability in steering than Conventional Tire 301 and exhibited a
large scattering in the gauge owing to significant rubber flow.
Comparative Tire 302 produced by using a butadiene rubber having
high impact resilience underwent unfavorable rubber flow and
exhibited poor stability in steering, even though it was lowered in
rolling resistance. Comparative Tire 303 produced by using an
increased amount of carbon fiber exhibited high rolling resistance
and poor durability in high-speed running, even though improved in
stability in steering.
[0164] Invention Tire 301 was improved in the prevention of rubber
flow by virtue of the addition of the short fiber (A), and was
therefore able to be lowered in rolling resistance with the
stability in steering being kept at improved in the prevention of
rubber flow by virtue of the addition of an increased amount of the
short fiber (A), and were therefore able to exhibit further
improved stability in steering. Comparative Tire 304 was poor in
stability in steering, because only the nylon short fiber (B) was
added to the under tread. With respect to Comparative Tire 305, the
rubber composition exhibited too high a Mooney viscosity to attain
good processability in extrusion as a result of the existence of
too large an amount of the nylon fiber (B) With respect to
Invention Tires 304 and 305, the hybridization of the short fiber
(A) with the nylon short fiber (B) became possible, because the
addition of the short fiber (A) gave a rubber composition having a
low Mooney viscosity. Thus, Invention Tires 304 and 305 were able
to be improved in durability in high-speed running. With respect to
Comparative Tire 306, the rubber composition was poor in
processability in extrusion because of the existence of too large
an amount of the short fiber (A).
EXAMPLE 4
[0165] Invention Tires 401 to 412 and Comparative tires 401 and 402
were produced, wherein at least a part of the sidewall was made of
a rubber composition containing a short fiber (A') formed by the
fibrillation of a short fiber (A) whose cross section took a
sea-island structure essentially composed of polyvinyl alcohol and
cellulose acetate (at a ratio of 60:40), and if necessary, a
composition wherein a short fiber (B) made of nylon 6 having amido
groups in the main chain was dispersed in a rubber matrix and
chemically bonded to the matrix. Further, Conventional Tires 401
and 402 were also produced, which did not contain any short fiber
in the sidewall. The sizes of these tires were 185/65R14. In
producing these test tires, the short fibers (A) and (B) were used
in various amounts per 100 parts by weight of the rubber. The
formulation of the rubber composition constituting the sidewalls of
the tires is given in Table 6.
6 TABLE 6 Amt. (pt. wt.) NR.sup.1) 50 BR.sup.2) 50 carbon black
(FEF class).sup.3) 50 stearic acid.sup.4) 2 zinc oxide.sup.5) 3
sulfur.sup.6) 2 vulcanization accelerator (NS).sup.7) 1 age
resister (RD).sup.8) 2 age resister (6C).sup.9) 3 aromatic
oil.sup.10) 5 .sup.1)RSS #1 .sup.2)a product of Nippon Zeon Co.,
Ltd., Nipol 1220 .sup.3)a product of Chubu Carbon, HTC100 .sup.4)a
product of Kao Corporation, Lunac YA .sup.5)a product of Toho Zinc
Co., Ltd., Ginrei zinc flower .sup.6)a product of karuizawa
Seiren-sho, powdered sulfur .sup.7)a product of Ohuchi Shinko
Kagaku, Nocceler NS-F .sup.8)a product of Ohuchi Shinko Kagaku,
Nocrac 224 .sup.9)a product of Ohuchi Shinko Kagaku, Nocrac 6C
.sup.10)a product of Nippon Oil Co., Ltd., Komorex 300
[0166] These test tires were evaluated for resistances to external
damage and crack growth, and the results are given in Tables 7 and
8. The average lengths of the short fiber (A), the average
diameters of the short fiber (A) after fibrillation and the
specific constitutions of the tires are also given in Tables 7 and
8. The positions of upper and lower ends of the short fiber
reinforced rubbers are given in terms of ratios of the heights of
the upper and lower ends from the bead heel to the tire sectional
height SH.
[0167] Resistance to External Damage:
[0168] Test tires were put on wheels having rim sizes of
14.times.5.multidot.1/2 JJ, and the air pressure was adjusted to
200 kpa. The resulting assemblies, were mounted on an automobile
having an engine displacement of 1600 cc block made of steel at an
approach angle of 30.degree. with the speed being gradually
enhanced from 10 km/h in steps of 1.0 km/h. The critical speed up
to which the tire did not burst was measured three times and the
average of the three values was calculated. The results are shown
by "X" referring to the case wherein the average critical speed is
lower than that of Conventional Tire 401, ".largecircle." referring
to the case wherein the average critical speed is higher than that,
of Conventional Tire 401 and ".circleincircle." referring to the
case wherein it is higher than that of Conventional Tire 401 by 2
km/h or above.
[0169] Resistance to Crack Growth:
[0170] A cut having a length of 5 mm and a depth of 1.5 mm was made
with a knife on the sidewall face of each test tire at an angle of
45.degree. to the radial direction. The resulting tire was put on a
wheel having rim sizes of 14.times.5.multidot.1/2. The resulting
assembly was mounted on a steel drum tester having a diameter of
1707 mm and a smooth surface. After 5000-km traveling under the
conditions of air pressure of 180 kPa, load of 3.74 kN and speed of
81 km/h, the length of the resulting cut was measured. The results
are given by "X" referring to the case wherein the length of the
cut exceeds 10 mm, ".largecircle." referring to the case wherein
the length is 10 mm or below, and ".circleincircle." referring to
the case where in the length is 0.8 mm or below.
7 TABLE 7 Conven- Conven- Comp. Invention tional tional Tire
Invention Invention Invention Invention Tire Tire 401 Tire 402 401
Tire 401 Tire 402 Tire 403 Tire 404 405 Formulation of sidewall
rubber NR (pt. wt.) 50 50 50 50 50 50 50 50 BR (pt. wt.) 50 50 50
50 50 50 50 50 short fiber (A) (pt. wt.) -- -- 0.3 0.5 15 5 5 5
short fiber (B) (pt. wt.) -- -- -- -- -- -- -- -- Short fiber (A)
av. length (.mu.m) -- -- 2000 2000 2000 1 5000 2000 av. diam. after
fibrillation (.mu.m) -- -- 1 1 1 1 1 0.05 Tire constitution
(sidewall) arrangement of short fiber -- -- reinforced rubber
thickness of rubber (not (mm) 3 2.5 0 0 0 0 0 0 containing short
fiber) thickness of fiber-reinforced rubber (mm) 0 0 2.5 2.5 2.5
2.5 2.5 2.5 total thickness of sidewall (mm) 3 2.5 2.5 2.5 2.5 2.5
2.5 2.5 percentage of thickness of (%) 0 0 100 100 100 100 100 100
fiber-reinforced rubber position of upper end of short fiber (%) --
-- 80 80 80 80 80 80 reinforced rubber position of lower end of
short fiber (%) -- -- 20 20 20 20 20 20 reinforced rubber tire mass
(g) 7300 7150 7150 7150 7150 7150 7150 7150 Test results resistance
to (acceptable or not) .largecircle. X X .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. external
damage resistance to (acceptable or not) .circleincircle.
.circleincircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. crack growth
[0171]
8 TABLE 8 Invention Comp. Invention Invention Invention Invention
Invention Invention Tire 406 Tire 402 Tire 407 Tire 408 Tire 409
Tire 410 Tire 411 Tire 412 Formulation of sidewall rubber NR (pt.
wt.) 50 50 50 50 50 50 50 50 BR (pt. wt.) 50 50 50 50 50 50 50 50
short fiber (A) (pt. wt.) 5 -- 0.5 0.5 10 10 5 5 short fiber (B)
(pt. wt.) -- 15 1 15 1 15 -- -- Short fiber (A) av. length (.mu.m)
2000 -- 2000 2000 2000 2000 2000 2000 av. diam. after fibrillation
(.mu.m) 5 -- 1 1 1 1 1 1 Tire constitution (sidewall) arrangement
of short fiber reinforced rubber thickness of rubber (not
containing short fiber) 0 0 0 0 0 0 1.5 1.5 thickness of
fiber-reinforced rubber 2.5 2.5 2.5 2.5 2.5 2.5 1 1 total thickness
of sidewall 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 percentage of thickness
of fiber-reinforced rubber 100 100 100 100 100 100 40 40 position
of upper end of short fiber reinforced rubber 80 80 80 80 80 80 80
80 (%) 20 20 20 20 20 20 20 20 position of lower end of short fiber
reinforced rubber 7150 7150 7150 7150 7150 7150 7150 7150 (%) tire
mass Test results resistance to external damage (acceptable or not)
.largecircle. X .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. resistance to crack
growth (acceptable or not) .largecircle. .largecircle.
.circleincircle. .circleincircle. .circleincircle. .circleincircle.
.largecircle. .largecircle.
[0172] short fiber (A). Comparative Tire 402 contained in the side
wall the short fiber (B) not together with the short fiber (A) but
alone, so that the sidewall was unsatisfactorily reinforced and
exhibited poor resistance to external damage.
EXAMPLE 5
[0173] Invention Tires 501 to 507 were produced, which were
heavy-duty pneumatic radial tires each comprising a carcass layer
containing a plurality of carcass cords in a state arranged in the
tire radial direction and bridging a pair of, i.e., lefthand and
righthand bead portions with the tire widthwise end portions of the
carcass layer wound up around the bead cores respectively from the
tire inner side to the tire outer side, and short fiber reinforced
layers lying at least in the wound-up end portions of the carcass
layer. Further, Conventional Tire 501 was also produced, which was
a pneumatic radial tire as described above wherein the short fiber
reinforced layers were replaced by rubber reinforcement layers The
tire sizes of these tires were 11R22.5 14PR.
[0174] In producing Invention Tires 501 to 507, the ratio of the
tire circumferential modulus (b) of the short fiber reinforced
layers to the tire radial modulus (b) thereof (i.e., b/a ratio) was
varied by incorporating a short fiber (A') formed by the
fibrillation of a short fiber (A) whose cross section took a
sea-island structure essentially composed of polyvinyl alcohol and
cellulose acetate, and, if necessary a composition wherein a short
fiber (B) made of nylon 6 having amido groups in the main chain was
dispersed in a rubber matrix and chemically bonded to the matrix
into the rubber constituting the short fiber reinforced layers and
orienting the fibrillated short fiber (A') and the short fiber (B)
in a tire circumferential direction. Further, in producing
Invention Tires 501 to 507, the short fibers (A) and (B) were used
in various amounts per 100 parts by weight of the rubber.
[0175] These test tires were evaluated for durability in high-speed
running by the following testing method, and the results are given
in Table 9.
[0176] Durability in High-Speed Running:
[0177] Each test tire was mounted on a drum tester with the air
pressure adjusted to 700 kPa and subjected to the test of
durability in high-speed running according to JIS D4230 to measure
the distance covered until the bead portion got out of order. The
results are given in terms of indexes as calculated by taking the
distance of Conventional Tire 501 as 100. A larger index means more
excellent durability in high-speed running.
9 TABLE 9 Invention Invention Invention Invention Invention
Invention Conventional Invention Tire Tire Tire Tire Tire Tire Tire
501 Tire 501 502 503 504 505 506 507 Edge cover for carcass layer
(see Fig. 9) b/a 1.0 1.2 1.2 1.2 1.3 1.3 1.3 6.5 short fiber (A)
(pt. wt.) -- 0.5 0.5 0.5 0.5 0.5 0.5 10.0 short fiber (B) (pt. wt.)
-- -- -- -- 1.0 1.0 1.0 15.0 Edge cover for steel cord reinforced
layer (see Fig. 9) b/a 1.0 1.0 1.2 1.2 1.0 1.3 1.3 6.5 short fiber
(A) (pt. wt.) -- -- 0.5 0.5 -- 0.5 0.5 10.0 short fiber (B) (pt.
wt.) -- -- -- -- -- 1.0 1.0 15.0 Reinforcement for bead portion
(see Fig. 11) b/a 1.0 1.0 1.0 1.2 1.0 1.0 1.3 6.5 short fiber (A)
(pt. wt.) -- -- -- 0.5 -- -- 0.5 10.0 short fiber (B) (pt. wt.) --
-- -- -- -- -- 1.0 15.0 Durability in high-speed running 100 107.4
110.2 134.5 112.7 115.3 146.3 147.5
[0178] As apparent from the results given in Table 9, Invention
Tires 501 to 507 were able to be remarkably improved in durability
in high-speed running as compared with Conventional Tire 501, even
though the rubber volumes of bead portions of Invention Tires 501
to 507 were equivalent to that of Conventional Tire 501. In
particular, Invention Tires 504 to 507 whose short fiber reinforced
layers were prepared by the hybridization between the short fibers
(A) and (B) were remarkably improved in the durability.
EXAMPLE 6
[0179] Invention Tires 601 to 618 and Comparative Tires with bead
fillers on the outer peripheral sides of the bead cores. In this
production, the bead fillers were made by incorporating a short
fiber (A') formed by the fibrillation of a short fiber (A) whose
cross section took a sea-island structure essentially composed of
polyvinyl alcohol and cellulose acetate and, if necessary, a
composition wherein a short fiber (B) made of nylon 6 having amido
groups in the main chain was dispersed in a rubber matrix and
chemically bonded to the matrix into the rubber constituting the
bead fillers and orienting the short fibers (A') and (B) in a tire
circumferential direction, by which the ratio of the storage
modulus (b) of the bead fillers in the direction of orientation of
the short fiber to the tire radical modulus (a) thereof (i.e., b/a
ratio) was varied. Further, Conventional Tire 601 was also
produced, which was provided with bead fillers not containing any
short fiber but containing steel reinforcements lying in the
neighborhood thereof. The sizes of these tires were 185/60R14
91H.
[0180] In producing Invention Tires 601 to 618 and Comparative
Tires 601 to 609, the short fibers (A) and (B) were used in various
amounts per 100 parts by weight of the rubber. Further, in
producing these tires, the short fibers in the bead fillers were
oriented in a tire circumferential direction (FIG. 13), in a tire
axial direction (FIG. 14) or in a combination of both (FIG.
15).
[0181] These test tires were evaluated for comfortableness in
riding, stability in steering and a light weight by the following
testing methods, and the results are given in Tables 10 to 12.
[0182] Comfortableness in Ridding:
[0183] Test tires were put on wheels having rim sizes of
14.times.5.multidot.1/2 JJ, and the air pressure was adjusted to
200 kpa. The resulting assemblies were mounted on an automobile
having an engine displacement of 1800 cc., and the automobile was
evaluated for comfortableness in riding by five test drivers
according to a feeling test. The results are given in terms of
indexes as calculated by taking the comfortableness of Conventional
Tire 601 as 100. A higher value means more excellent
comfortableness in riding.
[0184] Stability in Steering:
[0185] Test tires were put on wheels having rim sizes of
14.times.5.multidot.1/2 JJ, and the air pressure was adjusted to
200 kPa. The resulting assemblies were mounted on an automobile
having an engine displacement of 1800 cc, and the automobile was
evaluated for stability in steering by five test drivers according
to a feeling test. The results are given in terms of indexes as
calculated by taking the stability in steering of Conventional Tire
601 as 100. A higher value means more excellent stability in
steering.
[0186] Lightweightness:
[0187] The weights of the test tires were measured, and the results
are given in terms of indexes as calculated by taking the inversed
number of the measured weight of Conventional Tire 601 as 100. A
larger index means a lighter tire.
10 TABLE 10 Conventional Comp. Tire Comp. Comp. Invention Invention
Invention Invention Invention Invention Tire 601 601 Tire 602 Tire
603 Tire 601 Tire 602 Tire 603 Tire 604 Tire 605 Tire 606 b/a (1.0)
3 3 3 5 5 5 10 10 10 short fiber (A) (pt. wt.) -- 2 2 2 4 4 4 15 15
15 short fiber (B) (pt. wt.) -- -- -- -- -- -- -- -- -- --
direction of orientation of not used axial circum- axial and axial
circum- axial and axial circum- axial and short fiber ferential
circum- ferential circum- ferential circum- ferential ferential
ferential steel reinforcement used not used not used not used not
used not used not used not used not used not used comfortableness
in riding 100 105 105 105 105 105 105 105 105 105 stability in
steering 100 96 96 97 101 101 102 106 106 107 lithtweightness 100
110 110 110 110 110 110 110 110 110
[0188]
11 TABLE 11 Comp. Comp. Comp. Invention Invention Invention
Invention Invention Invention Tire 604 Tire 605 Tire 606 Tire 607
Tire 608 Tire 609 Tire 610 Tire 611 Tire 612 b/a 3 3 3 5 5 5 10 10
10 short fiber (A) (pt. wt.) 2 2 2 3 3 3 10 10 10 short fiber (B)
(pt. wr.) 1 1 1 1 1 1 15 15 15 direction of orientation of axial
circum- axial and axial circum- aixal and axial circum- axial and
short fiber ferential circum- ferential circum- ferential circum-
ferential ferential ferential steel reinforcement not used not used
not used not used not used not used not used not used not used
comfortableness in riding 105 105 105 105 105 105 105 105 105
stability in steering 95 95 96 100 100 101 105 105 106
lightweightness 110 110 110 110 110 110 110 110 110
[0189]
12 TABLE 12 Comp. Comp. Comp. Invention Invention Invention
Invention Invention Invention Tire 607 Tire 608 Tire 609 Tire 613
Tire 614 Tire 615 Tire 616 Tire 617 Tire 618 b/a 2 2 2 6 6 6 5 5 5
short fiber (A) (pt. wt.) -- -- -- 5 5 5 3 3 3 short fiber (B) (pt.
wt.) 5 5 5 3 3 3 10 10 10 direction of orientation of axial circum-
axial and axial circum- axial and axial circum- axial and short
fiber ferential circum- ferential circum- ferential circum-
ferential ferential ferential steel reinforcement not used not used
not used not used not used not used not used not used not used
comfortableness in riding 105 105 105 105 105 105 105 105 105
stability in steering 98 98 99 102 102 103 107 107 108
lightweightness 110 110 110 110 110 110 110 110 110
[0190] As apparent from the results given in Tables 10 to 12,
Invention Tires 601 to 618 were able to be improved in
comfortableness in riding and reduced in weight as compared with
Conventional Tire 601 provided with steel reinforcements, with
their stability in steering being kept at levels equivalent or
superior to that of Conventional Tire 601. On the other hand,
Comparative Tires 601 to 609 were unsatisfactory in stability in
steering owing to poor anisotropy of the bead fillers.
* * * * *