U.S. patent application number 12/465463 was filed with the patent office on 2009-09-03 for method for forming a green tread rubber and a pneumatic tire formed by using the green tread rubber.
Invention is credited to Ikuji Ikeda.
Application Number | 20090218018 12/465463 |
Document ID | / |
Family ID | 35004171 |
Filed Date | 2009-09-03 |
United States Patent
Application |
20090218018 |
Kind Code |
A1 |
Ikeda; Ikuji |
September 3, 2009 |
METHOD FOR FORMING A GREEN TREAD RUBBER AND A PNEUMATIC TIRE FORMED
BY USING THE GREEN TREAD RUBBER
Abstract
In a method for forming a green tread rubber comprised of a cap
rubber layer which outer surface forms a tread surface and a base
rubber layer that adjoins the same inside thereof in the radial
direction, a cap rubber having a rubber component of
styrene/butadiene rubber or being a mixed rubber of natural rubber
and butadiene rubber is used as the cap rubber layer. The base
rubber layer is formed as an annular body in which a strap-like
rubber extruded body of wide width, which is extruded from a rubber
extruder and is cut into constant size, is wound around a molding
drum by a single round with their end portions in a circumferential
direction being joined with each other. The cap rubber layer is
formed as a strip layered body in which a long strap-like rubber
strip of narrow width, which is extruded from an rubber extruder,
is successively wound by overlapping the same on the annular body
in the circumferential direction and in a spiral manner. A
thickness T2 of the base rubber layer on a tire equator is defined
to be 0.05 to 0.7 times a thickness T0 of the green tread rubber on
the tire equator.
Inventors: |
Ikeda; Ikuji; (Kobe-shi,
JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
35004171 |
Appl. No.: |
12/465463 |
Filed: |
May 13, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11139786 |
May 31, 2005 |
7549453 |
|
|
12465463 |
|
|
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|
Current U.S.
Class: |
152/209.5 ;
156/123 |
Current CPC
Class: |
B29D 30/62 20130101;
B60C 11/005 20130101; B29D 30/60 20130101 |
Class at
Publication: |
152/209.5 ;
156/123 |
International
Class: |
B29D 30/52 20060101
B29D030/52; B60C 11/00 20060101 B60C011/00; B60C 1/00 20060101
B60C001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2004 |
JP |
2004-190046 |
Oct 20, 2004 |
JP |
2004-305565 |
Claims
1. A method for forming a green tread rubber composed of a cap
rubber layer of which outer surface forms a tread surface and a
base rubber layer adjoining to the radially inside of the cap
rubber layer, wherein the base rubber layer is made of a base
rubber, and the cap rubber layer is made of a cap rubber, the
method comprising the steps of: forming an annular base rubber
layer by winding a strap-like base rubber one turn around a molding
drum and jointing the circumferential end portions thereof with
each other, wherein the strap-like base rubber is extruded from a
rubber extruder and is cut into a certain length; and forming the
cap rubber layer by successively winding and overlapping a long
strip of the cap rubber in the circumferential direction and in a
spiral manner on the annular base rubber layer, wherein the long
strip is extruded from a rubber extruder and has a smaller width
than that of the strap-like base layer, wherein a thickness T2 of
the base rubber layer is 0.05 to 0.7 times a thickness T0 of the
green tread rubber measured at the tire equator, the rubber
component of the cap rubber comprises a styrene-butadiene rubber,
the rubber component of the base rubber comprises a
styrene-butadiene rubber, and the cap rubber after vulcanization
has a complex elastic modulus E1* of 5.0 to 9.0 MPa.
2. The method according to claim 1, wherein the base rubber after
vulcanization has a complex elastic modulus E2* larger than the
complex elastic modulus E1* of the cap rubber.
3. The method according to claim 1, wherein a hardness Hs1 of the
cap rubber after vulcanization is 60 to 90 degrees, and a hardness
Hs2 of the base rubber after vulcanization is such that the
difference |HS1-Hs2| between the hardness HS1 and hardness Hs2 is
not more than 10 degrees.
4. The method according to claim 1, wherein the strip of the cap
rubber has a width of 5 to 30 mm and a thickness of 0.5 to 3.0
mm.
5. The method according to claim 1, wherein the rubber component of
the cap rubber comprises not less than 80 parts by mass of the
styrene/butadiene rubber per 100 parts by mass of the rubber base
material.
6. A method for forming a green tread rubber composed of a cap
rubber layer of which outer surface forms a tread surface and a
base rubber layer adjoining to the radially inside of the cap
rubber layer, wherein the base rubber layer is made of a base
rubber, and the cap rubber layer is made of a cap rubber, the
method comprising the steps of: forming an annular base rubber
layer by winding a strap-like base rubber one turn around a molding
drum and jointing the circumferential end portions thereof with
each other, wherein the strap-like base rubber is extruded from a
rubber extruder and is cut into a certain length; and forming the
cap rubber layer by successively winding and overlapping a long
strip of the cap rubber in the circumferential direction and in a
spiral manner on the annular base rubber layer, wherein the long
strip is extruded from a rubber extruder and has a smaller width
than that of the strap-like base layer, wherein a thickness T2 of
the base rubber layer is 0.05 to 0.7 times a thickness T0 of the
green tread rubber measured at the tire equator, the rubber
component of the cap rubber consists of 30 to 70 parts by mass of a
natural rubber and 70 to 30 parts by mass of a butadiene rubber,
the rubber component of the base rubber consists of 30 to 70 parts
by mass of a natural rubber and 70 to 30 parts by mass of a
butadiene rubber, and the cap rubber after vulcanization has a
complex elastic modulus E1* of 2.0 to 5.0 MPa.
7. The method according to claim 6, wherein the base rubber after
vulcanization has a complex elastic modulus E2* larger than the
complex elastic modulus E1* of the cap rubber.
8. The method according to claim 6, wherein a hardness HS1 of the
cap rubber after vulcanization is 40 to 60 degrees, and a hardness
Hs2 of the base rubber after vulcanization is larger than the
hardness Hs1.
9. The method according to claim 6, wherein the strip of the cap
rubber has a width of 5 to 30 mm and a thickness of 0.5 to 3.0
mm.
10. A pneumatic tire formed by using the green tread rubber
obtained through the method as claimed in any one of claims 1-9.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a 37 C.F.R. .sctn. 1.53(b)
divisional of U.S. application Ser. No. 11/139,786 filed May 31,
2005, which in turn claims priority on Japanese Application No.
2004-190046 filed Jun. 28, 2004 and Japanese Application NO.
2004-305565 filed Oct. 20, 2004. The entire contents of each of
these applications is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a method for forming a
green tread rubber with which it is possible to form, at high
quality, a green tread rubber of double-layered structure comprised
of a base rubber layer and a cap rubber layer, and a pneumatic tire
formed by using the green tread rubber.
[0003] It is common practice with pneumatic tires to employ a
double-layered structure for the tread rubber comprised of an inner
base rubber layer and a cap rubber layer outside thereof for
improving durability, steering stability, grip performances and
tire performances such as low rolling resistance.
[0004] Styrene/butadiene type rubber that exhibits superior aging
resistance, heat resistance, wear resistance and wet skid
resistance is employed as the cap rubber layer. On the other hand,
natural rubber type rubber that exhibits repulsive elasticity and
low heat-generating properties is employed as the base rubber
layer.
[0005] For instance, in case of high-performance tires that exhibit
superior high-speed running performances and winter tires that
exhibit superior on-snow performances employ styrene/butadiene
rubber as a rubber component for the cap rubber layer. With this
arrangement, properties such as the above heat resistance, wear
resistance and wet skid resistance are improved. In case of winter
tires, mixed rubber of natural rubber and butadiene rubber
exhibiting superior wear resistance and low temperature properties
is employed as the rubber component of the cap rubber layer.
[0006] In this respect, it is assumable to set a complex elastic
modulus E2* of the base rubber layer to be larger than a complex
elastic modulus E1* of the cap rubber layer. With this arrangement,
it is expected to improve the tread rigidity, to improve the
steering stability when performing high-speed running or the
steering stability on icy and snowy roads or when running on
general roads.
[0007] On the other hand, green tread rubber prior to vulcanization
molding for forming such tread rubber is conventionally
manufactured in the following manner. More particularly, as
illustrated in FIG. 5(A) in conceptual form, a molded body c of
double-layered structure is successively extruded from a rubber
extruder a. The molded body c of double-layered structure is cut
into constant size to meet a peripheral length of a molding drum D.
The cut rubber bodies c1 of constant size are once stored by being
accumulated in a multi-staged manner on a storage carrier e. When
molding a tire, the storage carrier e is transferred to a tire
molding line for supplying the rubber extruded bodies c1 to the
molding drum D. The rubber extruded bodies c1 are wound around the
molding drum D by a single round. End portions f, f in a
circumferential direction are mutually abutted and joined. With
this arrangement, a green tread rubber t for green tire molding is
formed in an annular shape. In this respect, reference g in the
drawing denotes a cooling line.
[0008] However, in such a conventional method, adhesive force
between the end portions f, f tends to fall short. Owing to this
fact, an opening tends to be generated at joint portions j of the
green tread rubber t in the course of manufacturing a tire.
Particularly in case the base rubber is made highly elastic as in
the above-described case, the adhesiveness of rubber is apt to be
degraded accompanying the high elasticity. The lack in adhesiveness
at the base rubber layer originates in and promotes the opening at
the cap rubber layer. This accordingly leads to degradations in
yield ratio and tire quality. When using styrene/butadiene rubber,
such rubber itself tends to be inferior in adhesiveness when
compared to natural rubber or the like, and the tendency of
occurrence of opening is stronger.
[0009] Thus, when joining the end portions f, f, it might happen at
the cap rubber layer t1 that the end portions f, f are not
sufficiently adhered as illustrated in FIG. 5(B). It might thus
happen that the joint portions j open in the course of
manufacturing a tire. It might also happen that the joint portions
j comprise weak points from which cracks occur. In case of
styrene/butadiene type rubber, it exhibits easily shrinking
properties. Dimensional changes (reductions in length) of the
rubber extruded bodies c1 during storage are accordingly large,
which promotes the opening or occurrence of cracks. Such opening
and occurrence of cracks become particularly remarkable when the
blending amount of styrene/butadiene rubber in styrene/butadiene
type rubber is increased to not less than 80 parts by mass for the
purpose of improving the tire performance.
[0010] The inventors of the present invention have thus suggested
forming only the base rubber layer by means of a rubber extruded
body from a rubber extruder while the cap rubber layer, which
exhibits inferior adhesiveness, is formed through a so-called
strip-wind method in which a tape-like rubber strip is overlapped
and successively wound around the base rubber layer in a
circumferential direction and in a spiral manner.
[0011] According to this method, it will be possible to reliably
prevent opening or cracks at the cap rubber also when the blending
amount of styrene/butadiene rubber is high and to improve the yield
ratio and the tire quality. In the green tread rubber, the rubber
composition of the cap rubber layer is changed in accordance with
types of tires and other factors. The method in the prior art
increased intermediate stock, since the cap rubber layer and the
base rubber layer are integrally extruded whereby it will be
required to change the rubber and to newly form double-layered
rubber extruded bodies c1. However, according to the present
invention, the cap rubber layer and the base rubber layer are
separately formed so that the base rubber layer can be standardized
to some extend or partially, and it will be possible to reduce the
volume or types of intermediate stock, since it may be required to
change rubber of, for instance, the rubber strip only.
[0012] In this respect, the inventors of the present invention have
suggested, in published patent application 2002-127718, winding a
soft rubber strip onto an inner layer in case of carcass rubber
rather than tread rubber. However, this suggestion concerns a
technique related to soft carcass rubber that is employed at
carcass portions. It is accordingly assumed that a soft rubber
strip having a required specified hardness, degree of tension, and
Mooney viscosity is employed.
BRIEF SUMMARY OF THE INVENTION
[0013] The present invention aims to provide a method for forming a
green tread rubber with which it is possible to reliably prevent
opening and cracks formed in the cap rubber layer, to improve the
yield ratio and tire quality, and to achieve remarkable cuts in
volume and types of intermediate stocks; to provide a method for
manufacturing a pneumatic tire formed by using the green tread
rubber; and to provide a pneumatic tire formed by using the green
tread rubber.
[0014] According to the present invention, there is provided a
method for forming a green tread rubber comprised of a cap rubber
layer which outer surface forms a tread surface and a base rubber
layer that adjoins the same inside thereof in the radial
direction,
[0015] wherein a cap rubber having a rubber component of
styrene/butadiene rubber or being a mixed rubber of natural rubber
and butadiene rubber is used as the cap rubber layer,
[0016] wherein the base rubber layer is formed as an annular body
in which a strap-like rubber extruded body of wide width, which is
extruded by a rubber extruder and is cut into constant size, is
wound around a molding drum by a single round with their end
portions in a circumferential direction being joined with each
other,
[0017] wherein the cap rubber layer is formed as a strip layered
body in which a long strap-like rubber strip of relatively narrow
width, which is extruded from an rubber extruder, is successively
wound by overlapping the same on the annular body in the
circumferential direction and in a spiral manner, and
[0018] wherein a thickness T2 of the base rubber layer on a tire
equator is defined to be 0.05 to 0.7 times a thickness T0 of the
green tread rubber on the tire equator.
[0019] With this arrangement, it is possible to reliably prevent
opening or cracks in the green tread rubber of double-layered
structure and to improve the yield ratio and tire quality. It is
also possible to achieve remarkable cuts in volumes and types of
intermediate stocks.
[0020] The base rubber layer may consist of a natural rubber type
rubber with natural rubber being blended d by not less than 50
parts by mass to a rubber base material, and the cap rubber layer
may consist of styrene/butadiene type rubber with styrene/butadiene
rubber being blended by not less than 80 parts by mass to a rubber
base material.
[0021] The base rubber layer may have a rubber component that is
identical to that of the cap rubber, and it is also possible to use
a base rubber which complex elastic modulus E2* after vulcanization
is larger than a complex elastic modulus E1* of the cap rubber
after vulcanization.
[0022] In this respect, the complex elastic moduli E* are values
obtained by measuring samples by using a viscoelasticity
spectrometer manufactured by Iwamoto Seisakusho Co., Ltd. under
conditions for the temperature being 70.degree. C., for the
frequency 10 HZ, or the initial stretch strain being 10%, and for
an amplitude of dynamic strain being .+-.2%. A rubber hardness HS
is a durometer A hardness measured by using a durometer type A in
conformity with JIS-K 6253.
[0023] In this context, the term "rubber components of identical
type" includes a case in which rubber is made of completely
identical rubber components and also a case in which monomer
sequences and/or microstructures differ while chemical structure
frames are identical. For instance, in case of styrene/butadiene
rubber (SBR), solution polymerized SBR (S-type) and emulsion
polymerized SBR (E-type) are rubber of identical type, and in case
of butadiene rubber (BR), high-cis 1,4 BR and low-cis 1, 4 BR are
rubber of identical type.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0024] FIG. 1 is a sectional view illustrating one embodiment of a
pneumatic tire employing green tread rubber formed by the forming
method according to the present invention;
[0025] FIG. 2 is a sectional view illustrating green tread rubber
employed for this purpose;
[0026] FIG. 3 is a diagram illustrating the forming method of the
present invention in conceptual form;
[0027] FIG. 4 is a sectional view illustrating one example of a
rubber strip; and
[0028] FIG. 5(A) is a diagram for explaining a conventional method
for forming a green tread rubber, and FIG. 5(B) is a sectional view
of joint portions for explaining a problematic point thereof.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] A first embodiment of the present invention will now be
explained on the basis of illustrated examples. FIG. 1 is a
sectional view illustrating a pneumatic tire employing green tread
rubber as formed by the forming method according to the present
invention.
[0030] In FIG. 1, the pneumatic tire 1 comprises a carcass 6 that
extends from a tread portion 2 over sidewall portions 3 up to bead
cores 5 of bead portions 4, and a belt layer 7 that is disposed
inside of the tread portion 2 and outside of the carcass 6 in the
radial direction.
[0031] The carcass 6 is comprised of at least one carcass ply
(wherein one carcass ply 6A is employed in the present embodiment)
in which carcass cords are aligned at angles of, for instance, 70
to 90.degree. with respect to a tire circumferential direction, and
while organic fiber cords such those made of nylon, polyester,
rayon or aromatic polyamide are favorably employed as the carcass
cords, it is also possible to employ metallic cords such as those
made of steel. The carcass ply 6A integrally includes ply turnup
portions 6b, which are turned up from inside to outside in a tire
axial direction around the bead cores 5 on both sides of a ply main
body portion 6a that bridges between the bead cores 5, 5, and a
bead apex rubber 8 for bead reinforcing purposes, which extends
outside from the bead cores 5 in the tire radial direction in a
tapered manner, is disposed between the ply main body portion 6a
and the turnup portions 6b.
[0032] The belt layer 7 is comprised of at least two belt plies
(wherein two belt plies 7A, 7B are employed in the present
embodiment) in which belt cords of high strength made, for
instance, steel cords, are disposed at angles of approximately 10
to 35.degree. with respect to the tire circumferential direction,
wherein the belt rigidity is improved through the belt cords
intersecting with each other between the plies so that
substantially the entire width of the tread portion 2 is firmly
reinforced through hoop effects.
[0033] It is also possible to provide a known band layer (not
shown) outside of the belt layer 7 in the radial direction in which
band cords of organic fiber such as nylon are aligned at angles of
not more than 5 degrees with respect to the circumferential
direction for the purpose of particularly improving high-speed
durability, and hereinafter, the band layer and the belt layer 7
are generally referred to as a tread reinforcing cord layer 9.
[0034] A tread rubber TG that comprises the tread portion 2 is
disposed outside of the tread reinforcing cord layer 9 in the
radial direction, wherein the tread rubber TG is arranged as a
double-layered structure comprised of a base rubber layer G2 that
adjoins the tread reinforcing cord layer 9 and a cap rubber layer
G1 that adjoins the same outside in the radial direction and which
outer surface comprises a tread surface 2s.
[0035] Here, styrene/butadiene type rubber (SBR type rubber), which
exhibits superior aging resistance, heat resistance, wear
resistance and wet skid resistance is employed as the cap rubber
layer G1. The SBR type rubber is arranged in that styrene/butadiene
rubber (SBR) is blended by not less than 80 parts by mass to 100
parts by mass of a rubber base material. Further, natural rubber
(NR) or butadiene rubber (BR) is favorably employed as the
remaining part of rubber. The SBR type rubber is capable of
improving durability of the tire, wear life and gripping
performances due to the above properties.
[0036] On the other hand, natural type rubber (NR type rubber)
exhibiting repulsive elasticity, low heat-generating properties and
adhesiveness is employed as the base rubber layer G2. The NR type
rubber contains not less than 50 parts by mass, preferably not less
than 60 parts by mass, and more preferably not less than 70 parts
by mass of natural rubber (NR). BR is favorably employed as the
remaining part of rubber. Thanks to the above properties, the NR
type rubber improves steering stability, low rolling resistance and
high-speed durability and also restricts separation from the tread
reinforcing cord layer 9.
[0037] In this respect, the rubber hardness Hs1 of the SBR type
rubber after vulcanization is defined to be 50 to 80.degree.. The
rubber hardness Hs2 of the NR type rubber after vulcanization is
defined to be smaller than the rubber hardness Hs1 of the SBR type
rubber, and a difference |Hs1-Hs2| is defined to be not less than
5.degree.. This arrangement is favorable in view of simultaneous
pursuit of grip performance and low rolling resistance.
[0038] A complex elastic modulus E1* of the SBR type rubber after
vulcanization is defined to be 5.0 to 8.0 MPa. A complex elastic
modulus E2* of the NR type rubber after vulcanization is set to be
smaller than the complex elastic modulus E1* of the SBR type
rubber, and a difference |E1*-E2*| is defined to be not less than
2.0 MPa. This arrangement is favorable in view of simultaneous
pursuit of durability and adhesiveness.
[0039] A tangential loss tand1 of the SBR type rubber after
vulcanization is set in a range of 0.10 to 0.30. A tangential loss
tand2 of the NR type rubber after vulcanization is defined to be
not more than 60% thereof, preferably not more than 50%, and
further to be not more than 40%, with this arrangement, it will be
possible to achieve simultaneously pursuit of steering stability
and low rolling resistance.
[0040] It is now assumed that a green tread rubber tg (FIG. 2) for
forming such as a tread rubber TG is manufactured by the above
conventional method (FIG. 5(A)). In such a case, the adhesiveness
of the SBR type rubber will be degraded which leads to a drop in
yield ratio of products owing to openings or cracks formed at the
joint portions j of the cap rubber layer G1 and to degradations in
tire quality.
[0041] The present invention thus forms the green tread rubber tg
by the following method. More particularly, as illustrated in FIG.
3 in conceptual form, a strap-like molded body c of single-layered
structure of large width that is made of a base rubber is
successively extruded from a rubber extruder a. Rubber extruded
bodies c1 that are obtained by cutting the molded bodies c into
constant size are wound by a single round around a molding drum D
on a tire molding line. Respective end portions f, f in a
circumferential direction are abutted and joined whereupon the base
rubber layer G2 is formed as an annular body 10. In this respect,
the present embodiment illustrates a case in which the molded body
c from the rubber extruder a is wound up by a reel r and is once
stored as discussed above. When molding a tire, the roll-like
molded body c is transferred to the tire molding line and is cut
into rubber extruded bodies c1 of constant size to be supplied to
the molding drum D. However, instead of storage in a roll-like
manner, it is also possible to perform cutting into rubber extruded
bodies c1 of constant size that are then stored by accumulating
them on a storage carriage in a multi-staged manner.
[0042] A lengthy strap-like rubber strip 11 of small width made of
cap rubber extruded from a rubber extruder m is employed as the cap
rubber layer G1. The rubber strip 11 is formed, as illustrated in
FIG. 2, by a strip laminated body 12 that is successively wound in
a circumferential direction upon overlapping them in a spiral
manner on the annular body 10.
[0043] Since the rubber strip 11 is successively wound in the tire
circumferential direction in such a trip laminated body 12, no
joint portions directed to cross the tire axial direction will be
formed in the cap rubber layer G1. Accordingly, also in case a SBR
type rubber having a high blending amount of SBR of not less than
80 parts by mass is employed as the cap rubber layer G1, opening of
the joint portions when molding a tire can be restricted. In this
respect, joint portions (interfaces) k are formed between adjoining
rubber strips 11, 11 in the tire axial direction in the strip
laminated body 12. However, the joint portions will be successive
in the circumferential direction. Additionally, since lateral force
acting in the tire axial direction is small when compared to
driving or braking force acting in the tire circumferential
direction in the tread portion 2, it will be possible to secure
sufficient strength.
[0044] In this respect, as illustrated in FIG. 4 in sectional form,
the rubber strip 11 has a strip width Ws of 5 to 30 mm and a strip
thickness Ts of 0.5 to 3.0 mm. Such an arrangement is convenient
for obtaining a green tread rubber tg having a desired sectional
shape.
[0045] In the above green tread rubber tg, a thickness T2 of the
base rubber layer G2 on a tire equator Co is required to be in a
range of 0.05 to 0.7 times a thickness T0 of the entire green tread
rubber tg on the tire equator Co. when this value exceeds 0.7
times, effects of improving road surface grip properties, wear
resistance and durability that are achieved by the cap rubber layer
G1 tends to be lost at an early stage with the base rubber layer G2
being exposed to the tread surface at an intermediate stage of
wear. When this value is less than 0.05, effects of improving low
rolling resistance and steering stability owing to the base rubber
layer G2 will not be sufficiently exhibited. In view of this fact,
it is preferable to set a lower limit value for a ratio T2/T0 of
the thickness to not less than 0.1, and further to not less than
0.15, and an upper limit value is preferably set to not more than
0.5 and further to not more than 0.3.
[0046] In the green tread rubber tg, for the purpose of enabling
the molded body c (not including a cap rubber layer G1) from the
rubber extruder a to be thin such that the thickness ratio T2/To is
not more than 0.7, the molded body c may be stored in a compact
roll-like manner in which it is wound up on the reel r as
illustrated in FIG. 3. As a result, it will be possible to perform
efficient storage by achieving cuts in storage space by, for
instance, approximately 20 to 30% when compared to a conventional
storage method in which storage is performed upon accumulation in a
multi-staged manner. Thanks to the thin molded body c, cooling can
also be easily performed so that the line length of the cooling
line g can be reduced to not more than 50% of a conventional line
length.
[0047] The roll-like molded body c can be sent out to the tire
molding line and supplied to the molding drum D while cutting the
same into rubber extruded bodies c1 of constant size. Accordingly,
no dimensional changes will be generated in the rubber extruded
bodies c1, and the annular body 10 (base rubber layer G2) can be
formed at high accuracy. In this respect, it is also preferable to
set the thickness T2 to not more than 6 mm for facilitating storage
of the molded body c in a roll-like condition.
[0048] While there are cases in which the rubber composition of the
cap rubber layer G1 is changed in accordance with types of tires or
the like in such a green tread rubber, since the cap rubber layer
G1 is formed separate from the base rubber layer G2 through a
strip-wind method, it is possible to standardize the molded body c.
In this case, only the rubber of the rubber strip needs to be
changed, and therefore it remarkably reduces the volume and types
of intermediate stock. At this time, a maximum width wc of the
rubber extruded bodies c1 in the tire axial direction is preferably
restricted to be not less than 0.6 times, preferably not less than
0.8 time and to not more than 1.2 times and preferably not more
than 1.1 times a tread width TW of a pneumatic tire after
vulcanization and molding. With this arrangement, it will be
possible to achieve standardization of the molded body c with
respect to tire sizes so that it is possible to achieve further
reductions in intermediate stocks.
[0049] The thus obtained green tread rubber tg is assembled to a
green tire in a conventionally known method, and by performing
vulcanization and molding of the molded green tire, the pneumatic
tire 1 as illustrated in FIG. 1 can be obtained. In this respect,
since methods for forming of parts other than the green tread
rubber are identical to those of the prior art, detailed
explanations thereof will be omitted here.
[0050] A second embodiment in which the pneumatic tire 1 is
employed as a high-performance tire oriented to high-speed running
performances will now be explained. This embodiment is of course
not to be limited to a high-speed running tire only. Matters other
than discussed in the present embodiment are in compliance with
those of the first embodiment.
[0051] The cap rubber layer G1 is formed of a cap rubber including
styrene/butadiene rubber (SBR) as a rubber component that exhibits
superior heat resistance, wear resistance and wet skid resistance.
Owing to the above properties of the SBR, the cap rubber layer G1
improves the high-speed durability, wear life and grip performance
of the tire.
[0052] The base rubber layer G2 has a rubber component, the type of
which is identical to that of the cap rubber layer G1, that is,
SBR. A base rubber G2 is formed of high elasticity which complex
elastic modulus E2* after vulcanization is larger than a complex
elastic modulus E1* of the cap rubber after vulcanization. By
forming the base rubber and the cap rubber of the same type rubber
components, the adhesive strength between both can be remarkably
improved. Since the base rubber is made to be highly elastic, it is
possible to sufficiently secure tread rigidity, to improve
responsiveness and response (sense of rigidity) of the steering
wheel which are strongly wanted for high-performance tires, and to
improve steering stability when performing high-speed running,
while exhibiting the above performances achieved by the cap rubber
layer G1. On the basis of types of rubber additives that are added
to the rubber components and differences in blending amounts, it is
possible to provide differences of the complex elastic moduli E1*,
E2* of the cap rubber and the base rubber.
[0053] In case of a high-performance tire, the complex elastic
modulus E1* of the cap rubber after vulcanization is preferably set
in a range of 5.0 to 9.0 MPa, a rubber hardness HS1 of the cap
rubber after vulcanization preferably to 60 to 90.degree., and a
difference between the same and the rubber hardness Hs2 of the base
rubber after vulcanization |HS1-Hs2| to no more than
10.degree..
[0054] Where the complex elastic modulus E1* is less than 5.0 MPa
and the rubber hardness HS1 is less than 60.degree., the cap rubber
layer G1 itself will be too soft so that it will be difficult to
achieve superior steering stability, even if the base rubber G2 is
made high elastic. Where the complex elastic modulus E1* is larger
than 9.0 MPa and the rubber hardness HS1 is larger than 90.degree.,
the cap rubber layer G1 will be too much hardened so that grounding
properties (grip performance and road following performances on the
road surface) are degraded and the riding comfort is harmed. When
the rubber hardness difference |Hs1-Hs2| exceeds 10.degree.,
drawbacks will be exhibited in that worsening of so-called
linearity is apt to occur in which behaviors of the vehicle when
performing, for instance, lane changing during high-speed running
become unstable.
[0055] A third embodiment in which the pneumatic tire 1 is
favorably employed as a winter tire exhibiting superior on-snow
running performances will now be explained. This embodiment is of
course not to be limited to a winter tire only. Matters other than
discussed in the present embodiment are in compliance with those of
the first embodiment.
[0056] The cap rubber layer G1 is formed of a cap rubber including
a mixed rubber of natural rubber (NR) and butadiene rubber (BR)
that exhibits superior wear resistance and low-temperature
properties as a rubber component. The cap rubber layer G1 is
capable of improving wear life and on-snow performances (grip
performances on icy and snowy road surfaces etc.) of the tire
through the above properties of the mixed rubber.
[0057] The base rubber layer G2 has a rubber component, the type of
which is identical to that of the cap rubber layer G1. That is, the
rubber component is formed of the mixed rubber, in the present
embodiment. A base rubber is of high elasticity which complex
elastic modulus E2* after vulcanization is larger than a complex
elastic modulus E1* of the cap rubber after vulcanization. By
forming the base rubber and the cap rubber of the same type of the
rubber components, the adhesive strength between both can be
improved. Since the base rubber is made to be highly elastic, it is
possible to sufficiently secure tread rigidity while exhibiting the
performances of the cap rubber layer G1. Accordingly, also in case
the cap rubber is made to be soft for achieving on-snow grip
performances, it is possible to maintain steering stability in that
the handle responsiveness and response (sense of rigidity) required
for running on general road surfaces can be sufficiently
secured.
[0058] In this respect, the mixed rubber is arranged in that 30 to
70 parts by mass of natural rubber and 70 to 30 parts by mass of
butadiene rubber are blended within 100 parts by mass of rubber
components, and the ratio between the natural rubber and butadiene
rubber can be varied within this range.
[0059] Here, in case of a winter tire, the complex elastic modulus
E1* of the cap rubber after vulcanization is preferably in the
range of 2.0 to 5.0 MPa, the rubber hardness HS1 of the cap rubber
after vulcanization is preferably in the range of 40 to 60.degree.,
and the rubber hardness Hs2 of the base member is larger than the
rubber hardness Hs1.
[0060] Where the complex elastic modulus E1* is less than 2.0 MPa
and the rubber hardness Hs1 is less than 40.degree., the cap rubber
layer G1 itself will be too soft so that it will be difficult to
achieve steering stability required for running on general road
surfaces however highly elastic the base rubber is made. Where the
complex elastic modulus E1* is larger than 5.0 MPa, the rubber
hardness Hs1 is larger than 60.degree., and Hs1>Hs2, the cap
rubber layer G1 will be too much hardened, and on-snow performances
cannot be exhibited owing to, for instance, degraded on-snow grip
performances.
[0061] In the second and third embodiments, the base rubber layer
G2 and the cap rubber layer G1 employ rubber of the same type of
rubber components. The adhesiveness between both layers will thus
be improved. Force of restricting movements of the end portions of
the base rubber layer G2 will thus strongly act such that effects
of restricting opening can be further improved.
[0062] In these alternative embodiments, the thickness T2 of the
base rubber layer G2 on the tire equator Co is required to be in
the range of 0.05 to 0.7 times the thickness T0 of the entire green
tread rubber tg on the tire equator Co. An upper limit thereof is
preferably set to not more than 0.6.
[0063] While preferred embodiments of the present invention have
been explained so far in details, the present invention is not
limited to the illustrated embodiments alone but may be embodied
upon modifying the same into various forms.
EXAMPLES
[0064] Pneumatic tires (Embodiment 1) having a tire size of
205/65R15 were manufactured by using the green tread rubber formed
by the method for forming according to the present invention, and
features such as presence/absence of occurrence of opening or
cracks in the tread rubber, the quality of the sample tires and the
productivity thereof in manufacturing were compared to those of
Comparative Examples 1A, 1B.
[0065] Investments, facility spaces, intermediate stock (storage)
spaces and expected amounts of intermediate stocks required for
establishing a green tread rubber forming line (FIG. 3) in which
the method for forming of the present invention can be performed
were compared to those of the comparative Examples 1A, 1B.
[0066] In this respect, in the Comparative Example 1, a
double-layered molded body c from the rubber extruder a was cut
into constant size, and the cut rubber bodies c1 of constant size
were stored as intermediate stocks by accumulating the same one on
a storage carriage e in a multi-staged manner. The storage carriage
e was transferred to the tire molding line, and the rubber extruded
bodies c1 were wound by a single round around the molding drum D to
form the green tread rubber in an annular manner. In the
Comparative Example 2, both of the base rubber layer and the cap
rubber layer were formed as laminated bodies of a rubber strip
using a strip-wind method.
(1) Occurrence of Openings or Similar:
[0067] Rates of occurrence of opening and cracks of the tread
rubber when manufacturing tires were calculated.
(2) Quality:
[0068] RFV of the sample tires were measured in conformity with the
uniformity testing method for vehicles according to JASO C607 by
using a uniformity tester, and reciprocals of average values of 100
tires were indicated as indices with that of the comparative
Example 1 being defined as 100. The larger the indices were, the
more favorable they were.
(3) Investments, Facility Spaces, Intermediate Stock (Storage)
Spaces and Amounts of Intermediate Stocks:
[0069] A green tread rubber forming line capable of producing two
types of tires at a ratio of 100 tires per 12 hours each was
assumed, and investments, facility spaces, intermediate stock
(storage) spaces and amounts of intermediate stocks were indicated
as indices with that of the Comparative Example 1 being 100. The
smaller the indices were, the more favorable they were.
TABLE-US-00001 TABLE 1 Comparative Comparative Example 1 Example 1A
Example 1b Cap rubber layer Rubber strip Rubber extruded Rubber
strip body (Integrated body) Base rubber layer Rubber Rubber strip
extruded body Occurrence of 0 5 0 opening Quality 145 100 150
Productivity 140 100 95 Investment 80 100 105 Facility space 50 100
45 Intermediate 20 100 15 stock space Intermediate 35 100 30 stock
amount
Alternative Example
[0070] Green tread rubber formed by the second and third
embodiments were employed for forming a high-performance tire
having a tire size of 215/45R17 (Embodiment 2) and a stud-less tire
having a tire size of 205/65R15 (Embodiment 3), and features such
as presence/absence of occurrence of opening or cracks in the tread
rubber and the productivity thereof in manufacturing were compared
to those of Comparative Examples 2A, 2B, 3A and 3B.
[0071] Investments, facility spaces, intermediate stock (storage)
spaces and expected amounts of intermediate stocks required for
establishing a green tread rubber forming line (FIG. 3) in which
the method for forming of the present invention can be performed
were compared to those of the Comparative Examples 2A, 2B, 3A and
3B.
[0072] In this respect, in the Comparative Examples 2A and 3A, a
double-layered molded body c from the rubber extruder a was cut
into constant size, and the cut rubber bodies c1 were stored as
intermediate stocks by accumulating the same one on a storage
carriage e in a multi-staged manner as illustrated in FIG. 5. The
storage carriage e was transferred to the tire molding line, and
the rubber extruded bodies c1 were wound by a single round around
the molding drum D to form the green tread rubber in an annular
manner. In the comparative Examples 2B and 3B, both of the base
rubber layer and the cap rubber layer were formed as laminated
bodies of a rubber strip using a strip-wind method.
(1) Occurrence of Openings or Similar:
[0073] Rates of occurrence of opening and cracks of the tread
rubber when manufacturing tires were calculated.
(2) Investments, Facility Spaces, Intermediate Stock (Storage)
Spaces and Amounts of Intermediate Stocks:
[0074] A green tread rubber forming line capable of producing two
types of tires at a ratio of 100 tires per 12 hours each was
assume, and investments, facility spaces, intermediate stock
(storage) spaces and amounts of intermediate stocks were indicated
as indices with that of the comparative Examples 2A and 3A being
100. The smaller the indices were, the more favorable they
were.
TABLE-US-00002 TABLE 2 Comparative Comparative Comparative
Comparative Example 2A Example 2B Example 2 Example 3A Example 3B
Example 3 Cap rubber layer Rubber Rubber strip Rubber strip Rubber
Rubber strip Rubber strip extruded body extruded body Rubber
component SBR SBR SBR NR + BR NR + BR NR + BR Complex elastic 7.5
7.5 7.5 4.0 4.0 4.0 modulus E1* <MPa> Rubber hardness Hs1 68
68 68 46 46 46 <degrees> Base rubber layer Rubber Rubber
strip Rubber Rubber Rubber strip Rubber extruded body extruded body
extruded body extruded body Rubber component SBR SBR SBR NR + BR NR
+ BR NR + BR Complex elastic 8.0 8.0 8.0 5.1 5.1 5.1 modulus E2*
<MPa> Rubber hardness Hs2 70 70 70 50 50 50 <degrees>
Rate of occurrence of 3 0 0 4 0 0 opening or similar <%>
Productivity 100 90 140 100 95 140 Investment 100 105 80 100 105 80
Facility space 100 45 50 100 45 50 Intermediate stock 100 15 20 100
15 20 space Intermediate stock 100 30 35 100 30 35 amount
* * * * *