CA1319091C - Pneumatic tires - Google Patents
Pneumatic tiresInfo
- Publication number
- CA1319091C CA1319091C CA000576198A CA576198A CA1319091C CA 1319091 C CA1319091 C CA 1319091C CA 000576198 A CA000576198 A CA 000576198A CA 576198 A CA576198 A CA 576198A CA 1319091 C CA1319091 C CA 1319091C
- Authority
- CA
- Canada
- Prior art keywords
- rubber
- tread
- layer portion
- expanded
- expanded rubber
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C11/00—Tyre tread bands; Tread patterns; Anti-skid inserts
- B60C11/14—Anti-skid inserts, e.g. vulcanised into the tread band
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C1/00—Tyres characterised by the chemical composition or the physical arrangement or mixture of the composition
- B60C1/0016—Compositions of the tread
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60C—VEHICLE TYRES; TYRE INFLATION; TYRE CHANGING; CONNECTING VALVES TO INFLATABLE ELASTIC BODIES IN GENERAL; DEVICES OR ARRANGEMENTS RELATED TO TYRES
- B60C11/00—Tyre tread bands; Tread patterns; Anti-skid inserts
- B60C11/0041—Tyre tread bands; Tread patterns; Anti-skid inserts comprising different tread rubber layers
- B60C11/005—Tyre tread bands; Tread patterns; Anti-skid inserts comprising different tread rubber layers with cap and base layers
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Tires In General (AREA)
Abstract
62-220,697 comb.
PNEUMATIC TIRES
Abstract of the Disclosure A pneumatic tire having excellent tire performances in winter and summer seasons comprises a tread, a part of which is comprised of an expanded rubber in a volume corresponding to at least 10% of the total volume of the tread at its surface. This expanded rubber contains particular rubber component and particular high reinforcing carbon black and oil, and has particular number of closed cells having a specified cell diameter to the total number of closed cells.
Furthermore, a rubber reinforcing layer is arranged near to the tread shoulder.
PNEUMATIC TIRES
Abstract of the Disclosure A pneumatic tire having excellent tire performances in winter and summer seasons comprises a tread, a part of which is comprised of an expanded rubber in a volume corresponding to at least 10% of the total volume of the tread at its surface. This expanded rubber contains particular rubber component and particular high reinforcing carbon black and oil, and has particular number of closed cells having a specified cell diameter to the total number of closed cells.
Furthermore, a rubber reinforcing layer is arranged near to the tread shoulder.
Description
62-220,697 comb.
PNEUMATIC TIRES
This invention relates to pneumatic tires, and more particularly to a pneumatic tire having consider-ably improved durability, ln which wear resistance is durable in practical use without damaging the corneriny 05 performances and heat durable performance in summer season as well as spring and autumn seasons (hereinafter referred to as summer season), and also ice and snow performances such as driving performance, braking performance, cornering performance and the like on ice and snow road surface in winter season are improved and further dynamic compression permanent deformation (so-called flattening resistance) and separation resistance are improved.
In the conventional pneumatic tires, in order to ensure the driving performance, braking performance and cornering performance during the running on ice and snow road surface (hereinafter referred to as ice-snow performances, simply), a chain is attached to the tire, or a spike tire obtained by striking spike pins into a surface portion of a tire tread is frequently used~
However, microparticles produced by wearing of the chain and spike pins or the wearing of the road are scattered to cause dust nuisance, or injury of road is caused by ~ 3 ~
the spike pins, which comes into a large social problem.
For this end, a so-called studless tire using no spike pin is recently proposed, and various investigatlons on the tread pattern and rubber material for such a 05 studless tire are made. However, the ice-snow performances of the studless tire are not yet developed up to a level equal to those o the spike tire.
Particularly, there are an attempt that in order to ensure rubbery elasticity at a low temperature, a 10 polymer having a low glass transition point is used as the rubber material for the tread, an attempt that a softening agent having a low melting point is used for ensuring the friction coefficient on road surface at a low temperature, and the like, but these attempts are 1~ still insufficient in the ice-snow performances.
On the other handr tires using an expanded rubber in the tread are proposed in ~apanese Patent Application Publication No. 40-4,641, Japanese Patent laid open No. 56-154,304 and US Patent 4,249,588.
In Japanese Patent Application Publication No. 40-4,641, however, a synthetic rubber having a large hysteresis loss such as high-styrene rubber is used in the tread, which raises the glass transition point of rubber to increase the hardness of rubber at a low temperature, so that it is unfavorable in view of the Ice-snow performances.
~ .
~ 3 ~ L
Further, Japanese Patent laid open No. 56-154,304 discloses a light wei~ht tire by using an expanded rubber so as to provide a hardness equal to that of nonexpanded rubber, which can not improve the OS ice-snow perormances.
~ oreover, when the tire using the expanded rubber in the tread is used over a long period on dry road surface and ice and snow road surface, the wearing of the tread rubber is fast and the wear resistance is not sufficient. In this connection, the improvement of the expanded rubber for solving the above problem has previously been proposed in Japanese Patent ~pplication No. 61-235,921, but it has been confirmed that the flattening resistance is not yet sufficient in practical use.
It is, therefoxe, an object of the invention to provide a pneumatic tire durable in practical use in which a tread rubber is composed of an expanded rubber containin~ a particular rubber component and a particular high-reinforcing caxbon black and having specific expansion ratio and cell diameter distribution to cause no flattening phenomenon and lessen the change of hardness of the expanded rubber with the lapse of time even if the tire is used on ice and snow road surface over a long period.
The inventors have made various studies in order ~ 3 ~
to solve the above problems and found the following points.
That is, in the tire tread having the expanded rubber layer, it has been found that a particular rubber composition obtained by compounding a proper amount oE
05 high reinforcing carbon black and a particular amount or less of an oil with a particular rubber component is effective as an expanded rubber in order to prevent the flattening phenomenon of blocks and maintain the wear resistance.
Further, it has been found that in the expanded rubber comprised of the above particular rubber composi-tion, the optimization of cell diameter distribution in the expanded rubber is more effective for the solution of the above problems.
1~ The inventors have made further investigations and as a result the invention has been accomplished.
According to the invention, there is provided a pneumatic tire comprising a tire casing and a tread covering a cro~n portion of said casing/ characterized in that said tread is provided at its surface side with an expanded rubber layer in a volume corresponding to at least 10% of a total volume of said tread; and said expanded rubber layer is comprised of an e~panded rubber containing not less than 50 parts by weight of at least 2~ one rubber component selected from natural rubber, ~ 3 ~
polybutadiene rubber and styrene butadiene copolymer rubber having a glass transition temperature of not higher than -45C, a high reinforcing carbon black having an N2SA of 90~1~0 m2/g and not more than 20 parts 05 by weight of an oil per 100 parts by weight of said rubber component; and said expanded rubber contains closed cells at an expansion ratio IVs) of 5~50% so that the number of closed cells having a cell diameter of 5~30 ~m is not less than 50% of total number of closed cells having a cell diameter of not less than 5 ~m per unit area as a whole of said expanded rubber.
In a preferred embodiment of the invention, the tread consists of an outer layer portion comprised of the expanded rubber layer and an inner layer portion and l~ is provided near to a shoulder thereof with a rubber reinforcing layer covering a first joint end part between the outer layer portion and the inner layer portion and a second joint end part between the inner layer portion and a sidewall portion.
The invention will be described with reference to the accompanying drawing, wherein:
A single f igure is a partial section view of an embodiment of the pneumatic tire according to the invention.
2~ ~ccording to the invention, it is necessary that at least one of natural rubber, polybutadiene rubber and 1 3 .~
styrene-butadiene copolymer rubber is contained in an amount of not less than 50 parts by weight as a rubber component. Preferably, the amount of polybutadiene rubber is not less than 20 parts by weight but not more 05 than 50 parts by welght. The reason why the rubber component is limited to the aforementioned rubbers is due to the fact that the tread containing such rubber has a sufficient rubber elasticity even at a low temperature.
Further, the reason why the N2SA of the high reinforcing carbon black is limited to 90~130 m2/g is based on the fact that when the N2SA is less than 90 m2/g or more than 180 m2/g, the effect of the invention can not be developed. Moreover, the value of 15 N2SA is measured according to a test method of ASTM
D3037-B. The amount of the high reinforcing carbon black is preferable to be 30~70 parts by weight per 100 parts by weight of the rubber component. When the amount is less than 30 parts by weight, the wear resistance is degraded, while when it exceeds 70 parts by weight, the processabiliky is degraded. As the high reinforcing carbon black, carbon blacks of ISAF and SAF
grades are desirable, and particularly carbon black SAF
is preferable.
The oil is added in an amount of not more than 20 parts by weight, preferably not more than 10 parts by ~L 3 ~
weight, more particularly not more than 5 parts by weight per 100 parts b~ weight of the rubber component.
In this case, the expanded rubber may contain no oil.
When the amount of the oil exceeds 20 parts by weight, 05 the wear resistance is degraded.
Furthermore, the expanded rubber layer is necessary to have a volume corresponding to at least 10%
of total volume o~ the tread. The volume of the expanded rubber layer is preferably within a range of 10 10~70~, particularly 40~60%. When the volume of the expanded rubber layer is less than 10%, the effect of improving the ice-snow performances is small.
According to the invention, the whole of the tread may be comprised of only the expanded rubber layer 1~ (i.e. 100% expanded rubber layer).
The expansion ratio Vs of the expanded rubber is represented by the following e~uation:
~s = {(P~~Pg)/(Pl~Pg) - 1} x 100 (%)...... (1~
where Pl is a density of the expanded rubber (g/cm3)~ pO
20 is a density of solid rubber phase portion in the expanded rubber (g/cm3) and pg is a density of gas portion in cells of the expanded rubber (g/cm ). That is, the expanded rubber is comprised of solid rubber phase portions and cavities formed by the solid rubber 2~ phase portion (closed cells) or gas portions in the cells. Since the density pg of the gas portion is very small and substantially approaches to zero and also i5 very small to the density Pl of the solid rubber phase portion, the above equation (l) is approximately equal to the following equation:
OG Vs = (Po/Pl ~ 1) x 100 (%) .. (2) ~ ccording to the invention, the expansion ratio Vs is within a range of 5~50%, preferably 5~30%. When the expansion ratio is less than 5~, the flexibllity of the expanded rubber is not developed at a low temperature, 10 while when it exceeds 50%l the wear resistance is degraded and becomes practically insufficient on ice and snow road surface as well as dry road surface.
In the expanded rubber according to the invention, the number of closed cells having a cell diameter of 5~30 lum, preferably 5~25 ~um is not less than 50% of total number of closed cells ha~ing a cell diameter of not less than 5 ~um per unit area as a whole of the e~panded rubber. The reason why the number of the closed cells having a cell diameter of 5~30 ~m is limited to not less than 50% of the total numker of the closed cells per unit area is due to the fact that when the cell diameter is less than 5 lum, the braking performance on ice road surface is degraded, while when it exceeds 30 ~m, the wear resistance is degraded and 2~ the flattening phenomenon is caused to degrade the appearance of the tire.
g ~ 3 ~
In general, when the tire as in the invention is used in a vehicle running on ice and snow road, it is liable to cause crack growth at a state of applying tension to the tire surface because the expanded rubber as is soft. That is, cut damage may be entered into the vicinity oE the tread shoulder through broken stones or pebble stones. If the tire is run after the attachment of a chain, damage or the like may be entered into the shoulder portion. From these damages, cracks may grow 10 and finally separation failure may be caused in the interior of the tire.
In this connection, the inventors have made various studies with respect to action of road surface to tread during the running, relation between function 1~ Of each part o~ the tread and properties thereof, occurrence of cut damage in the vicinity of the shoulder, position of generating separation failure, state of proceeding such failure and the like. As a result, it has been found that the tread is rendered into a two-layer structure of an outer layer portion and an inner layer portion to thereby divide the function thereof and also the balance in the properties between the outer layer portion and the inner layer portion is taken by adjusting the volume of the outer layer portion 2~ composed of the expanded rubber and making the modulus of elasticity of the inner layer portion large, whereby 1 3 ~
the cornering per~ormance and other per~ormances are improved. Further, it has been found that the occurrence and growth oE the failures can be prevented by coverin~ a join-t part between different rubbers in 05 the vicinity of the shoulder with a rubber reinorciny layer having adequate properties.
That is, in the preferred embodiment of the invention, the tread consists o~ an outer layer portion comprised of the e~panded rubber layer and an inner layer portion and is provided near to a shoulder thereo with a rubber reinforcing layer coverin~ a first joint end part between the outer layer portion and the inner layer portion and a second joint end part between the inner layer portion and a sidewall portion, whereby the 1~ function o~ the tread is divided and also the shoulder portion is reinforced to enhance the ice-snow per~orm-ances in winter season, various performances in summer season and the durability.
The reason why the tread is rendered into the two-layer structure of outer layer portion and inner layer portion is based on the fact that the hardness of the inner layer portion is made harder than ~hat of the outer layer portion to increase the rigidity of blocks as a surface pattern in the outer layer portion of the tread, 2~ whereby the performances on snow in winter season, cornering stability and braking performance on ice are ~, ~ 3 ~
improved and the performances between summer season and winter season can be simultaneously established.
Further, the hardness of the expanded rubber in the outer layer portion of the tread is within a range of o~ 35~59, preferably 43~53. When the tread rubber is made softer, the true ground contact area of the tread can be increased to enhance the performances on ice, but the rigidity of the blocks in the tread is reduced to degrade the cornering stability on snow.
On the other hand, the reason why the first and second joint end parts are covered with the rubber reinforcing layer is due to the fact that a non-expanded skin layer of about 0.3 ~m in thickness is usually exi~tent in the outer surface of the expanded rubber and 1~ the boundary between the expanded rubber and the other rubber. Further, the expanded rubber is poor in the resistance to crack growth under a tension as compared with the ordinary rubber, so that crack is particularly apt to be caused from a side face of the block located in the shoulder of the tread. That is, in the conventional tread of the two-layer structure, the expanded rubber having a skin layer of about 0.3 ~m is existent in the vicinity of the shoulder being most liable to be subjected to cut damage and the like, resulting in the degradation of separation resistance and cut resistance from the side face of the tread.
1 3 ~
on the contrary, in the invention, the rubber reinforcing layer is arranged to cover the skin layer of the expanded rubber in the shoulder and the joint end parts, whereby the cut resistance and separation o~ resistance are improved in the vicinity of the shoulder.
The expanded rubber in the tread of the pneumatic tire according to the invention is formed by adding an expanding agent to the usual rubber composi-tion and curing them according to the usual tire building process. ~s the expandiny agent for the expanded rubber, use may be made, for example, of azodicarbon amide, dinitrosopentamethylene tetramine, azobisisobutyronitrile, benzene sulphonyl hydxazide, oxybis-benzene sulphonyl hydrazide, microcapsule of high 1~ boiling hydrocarbon resin and the like. Preferably, the sulphonyl hydrazide compounds, particularly oxybis-benzene sulp~onyl hydrazide are used in view of fine expansion.
The following examples are given in illustration 2~ f the invention and are not intended as limitations thereof. In these examples, the properties of the expanded rubber and tire performances were evaluated by the following test methods.
(1) Expansion ratio Vs The expansion ratio Vs of the expanded rubber was determined according to the aformentioned equation 1 3 ~
(2) after a block-like specimen was cut out from the expanded rubber layer in the tread of the test tire and the density Pl (g/orn ) of the specimen was measured and the density pO of non-expanded rubber (solid phase o~ rubber) of the tread was measured.
(2) Cell diameter and number of closed cells The cell diameter and number of closed cells in the expanded rubber were determined as follows. That is, a block-like specimen was cut out from the expanded rubber layer in the tread of the test tire and the cut surface of the specimen was photographed by means of an optical microscope with a magnification of 100~400, from which the cell diameter of the closed cell was measured.
Then, the number of cells having a cell diameter of not 1~ less than 5 ~m was measured over a total area of 4 mm2 or more, from which the number of closed cells per unit area of l mm2 was calculated.
PNEUMATIC TIRES
This invention relates to pneumatic tires, and more particularly to a pneumatic tire having consider-ably improved durability, ln which wear resistance is durable in practical use without damaging the corneriny 05 performances and heat durable performance in summer season as well as spring and autumn seasons (hereinafter referred to as summer season), and also ice and snow performances such as driving performance, braking performance, cornering performance and the like on ice and snow road surface in winter season are improved and further dynamic compression permanent deformation (so-called flattening resistance) and separation resistance are improved.
In the conventional pneumatic tires, in order to ensure the driving performance, braking performance and cornering performance during the running on ice and snow road surface (hereinafter referred to as ice-snow performances, simply), a chain is attached to the tire, or a spike tire obtained by striking spike pins into a surface portion of a tire tread is frequently used~
However, microparticles produced by wearing of the chain and spike pins or the wearing of the road are scattered to cause dust nuisance, or injury of road is caused by ~ 3 ~
the spike pins, which comes into a large social problem.
For this end, a so-called studless tire using no spike pin is recently proposed, and various investigatlons on the tread pattern and rubber material for such a 05 studless tire are made. However, the ice-snow performances of the studless tire are not yet developed up to a level equal to those o the spike tire.
Particularly, there are an attempt that in order to ensure rubbery elasticity at a low temperature, a 10 polymer having a low glass transition point is used as the rubber material for the tread, an attempt that a softening agent having a low melting point is used for ensuring the friction coefficient on road surface at a low temperature, and the like, but these attempts are 1~ still insufficient in the ice-snow performances.
On the other handr tires using an expanded rubber in the tread are proposed in ~apanese Patent Application Publication No. 40-4,641, Japanese Patent laid open No. 56-154,304 and US Patent 4,249,588.
In Japanese Patent Application Publication No. 40-4,641, however, a synthetic rubber having a large hysteresis loss such as high-styrene rubber is used in the tread, which raises the glass transition point of rubber to increase the hardness of rubber at a low temperature, so that it is unfavorable in view of the Ice-snow performances.
~ .
~ 3 ~ L
Further, Japanese Patent laid open No. 56-154,304 discloses a light wei~ht tire by using an expanded rubber so as to provide a hardness equal to that of nonexpanded rubber, which can not improve the OS ice-snow perormances.
~ oreover, when the tire using the expanded rubber in the tread is used over a long period on dry road surface and ice and snow road surface, the wearing of the tread rubber is fast and the wear resistance is not sufficient. In this connection, the improvement of the expanded rubber for solving the above problem has previously been proposed in Japanese Patent ~pplication No. 61-235,921, but it has been confirmed that the flattening resistance is not yet sufficient in practical use.
It is, therefoxe, an object of the invention to provide a pneumatic tire durable in practical use in which a tread rubber is composed of an expanded rubber containin~ a particular rubber component and a particular high-reinforcing caxbon black and having specific expansion ratio and cell diameter distribution to cause no flattening phenomenon and lessen the change of hardness of the expanded rubber with the lapse of time even if the tire is used on ice and snow road surface over a long period.
The inventors have made various studies in order ~ 3 ~
to solve the above problems and found the following points.
That is, in the tire tread having the expanded rubber layer, it has been found that a particular rubber composition obtained by compounding a proper amount oE
05 high reinforcing carbon black and a particular amount or less of an oil with a particular rubber component is effective as an expanded rubber in order to prevent the flattening phenomenon of blocks and maintain the wear resistance.
Further, it has been found that in the expanded rubber comprised of the above particular rubber composi-tion, the optimization of cell diameter distribution in the expanded rubber is more effective for the solution of the above problems.
1~ The inventors have made further investigations and as a result the invention has been accomplished.
According to the invention, there is provided a pneumatic tire comprising a tire casing and a tread covering a cro~n portion of said casing/ characterized in that said tread is provided at its surface side with an expanded rubber layer in a volume corresponding to at least 10% of a total volume of said tread; and said expanded rubber layer is comprised of an e~panded rubber containing not less than 50 parts by weight of at least 2~ one rubber component selected from natural rubber, ~ 3 ~
polybutadiene rubber and styrene butadiene copolymer rubber having a glass transition temperature of not higher than -45C, a high reinforcing carbon black having an N2SA of 90~1~0 m2/g and not more than 20 parts 05 by weight of an oil per 100 parts by weight of said rubber component; and said expanded rubber contains closed cells at an expansion ratio IVs) of 5~50% so that the number of closed cells having a cell diameter of 5~30 ~m is not less than 50% of total number of closed cells having a cell diameter of not less than 5 ~m per unit area as a whole of said expanded rubber.
In a preferred embodiment of the invention, the tread consists of an outer layer portion comprised of the expanded rubber layer and an inner layer portion and l~ is provided near to a shoulder thereof with a rubber reinforcing layer covering a first joint end part between the outer layer portion and the inner layer portion and a second joint end part between the inner layer portion and a sidewall portion.
The invention will be described with reference to the accompanying drawing, wherein:
A single f igure is a partial section view of an embodiment of the pneumatic tire according to the invention.
2~ ~ccording to the invention, it is necessary that at least one of natural rubber, polybutadiene rubber and 1 3 .~
styrene-butadiene copolymer rubber is contained in an amount of not less than 50 parts by weight as a rubber component. Preferably, the amount of polybutadiene rubber is not less than 20 parts by weight but not more 05 than 50 parts by welght. The reason why the rubber component is limited to the aforementioned rubbers is due to the fact that the tread containing such rubber has a sufficient rubber elasticity even at a low temperature.
Further, the reason why the N2SA of the high reinforcing carbon black is limited to 90~130 m2/g is based on the fact that when the N2SA is less than 90 m2/g or more than 180 m2/g, the effect of the invention can not be developed. Moreover, the value of 15 N2SA is measured according to a test method of ASTM
D3037-B. The amount of the high reinforcing carbon black is preferable to be 30~70 parts by weight per 100 parts by weight of the rubber component. When the amount is less than 30 parts by weight, the wear resistance is degraded, while when it exceeds 70 parts by weight, the processabiliky is degraded. As the high reinforcing carbon black, carbon blacks of ISAF and SAF
grades are desirable, and particularly carbon black SAF
is preferable.
The oil is added in an amount of not more than 20 parts by weight, preferably not more than 10 parts by ~L 3 ~
weight, more particularly not more than 5 parts by weight per 100 parts b~ weight of the rubber component.
In this case, the expanded rubber may contain no oil.
When the amount of the oil exceeds 20 parts by weight, 05 the wear resistance is degraded.
Furthermore, the expanded rubber layer is necessary to have a volume corresponding to at least 10%
of total volume o~ the tread. The volume of the expanded rubber layer is preferably within a range of 10 10~70~, particularly 40~60%. When the volume of the expanded rubber layer is less than 10%, the effect of improving the ice-snow performances is small.
According to the invention, the whole of the tread may be comprised of only the expanded rubber layer 1~ (i.e. 100% expanded rubber layer).
The expansion ratio Vs of the expanded rubber is represented by the following e~uation:
~s = {(P~~Pg)/(Pl~Pg) - 1} x 100 (%)...... (1~
where Pl is a density of the expanded rubber (g/cm3)~ pO
20 is a density of solid rubber phase portion in the expanded rubber (g/cm3) and pg is a density of gas portion in cells of the expanded rubber (g/cm ). That is, the expanded rubber is comprised of solid rubber phase portions and cavities formed by the solid rubber 2~ phase portion (closed cells) or gas portions in the cells. Since the density pg of the gas portion is very small and substantially approaches to zero and also i5 very small to the density Pl of the solid rubber phase portion, the above equation (l) is approximately equal to the following equation:
OG Vs = (Po/Pl ~ 1) x 100 (%) .. (2) ~ ccording to the invention, the expansion ratio Vs is within a range of 5~50%, preferably 5~30%. When the expansion ratio is less than 5~, the flexibllity of the expanded rubber is not developed at a low temperature, 10 while when it exceeds 50%l the wear resistance is degraded and becomes practically insufficient on ice and snow road surface as well as dry road surface.
In the expanded rubber according to the invention, the number of closed cells having a cell diameter of 5~30 lum, preferably 5~25 ~um is not less than 50% of total number of closed cells ha~ing a cell diameter of not less than 5 ~um per unit area as a whole of the e~panded rubber. The reason why the number of the closed cells having a cell diameter of 5~30 ~m is limited to not less than 50% of the total numker of the closed cells per unit area is due to the fact that when the cell diameter is less than 5 lum, the braking performance on ice road surface is degraded, while when it exceeds 30 ~m, the wear resistance is degraded and 2~ the flattening phenomenon is caused to degrade the appearance of the tire.
g ~ 3 ~
In general, when the tire as in the invention is used in a vehicle running on ice and snow road, it is liable to cause crack growth at a state of applying tension to the tire surface because the expanded rubber as is soft. That is, cut damage may be entered into the vicinity oE the tread shoulder through broken stones or pebble stones. If the tire is run after the attachment of a chain, damage or the like may be entered into the shoulder portion. From these damages, cracks may grow 10 and finally separation failure may be caused in the interior of the tire.
In this connection, the inventors have made various studies with respect to action of road surface to tread during the running, relation between function 1~ Of each part o~ the tread and properties thereof, occurrence of cut damage in the vicinity of the shoulder, position of generating separation failure, state of proceeding such failure and the like. As a result, it has been found that the tread is rendered into a two-layer structure of an outer layer portion and an inner layer portion to thereby divide the function thereof and also the balance in the properties between the outer layer portion and the inner layer portion is taken by adjusting the volume of the outer layer portion 2~ composed of the expanded rubber and making the modulus of elasticity of the inner layer portion large, whereby 1 3 ~
the cornering per~ormance and other per~ormances are improved. Further, it has been found that the occurrence and growth oE the failures can be prevented by coverin~ a join-t part between different rubbers in 05 the vicinity of the shoulder with a rubber reinorciny layer having adequate properties.
That is, in the preferred embodiment of the invention, the tread consists o~ an outer layer portion comprised of the e~panded rubber layer and an inner layer portion and is provided near to a shoulder thereo with a rubber reinforcing layer coverin~ a first joint end part between the outer layer portion and the inner layer portion and a second joint end part between the inner layer portion and a sidewall portion, whereby the 1~ function o~ the tread is divided and also the shoulder portion is reinforced to enhance the ice-snow per~orm-ances in winter season, various performances in summer season and the durability.
The reason why the tread is rendered into the two-layer structure of outer layer portion and inner layer portion is based on the fact that the hardness of the inner layer portion is made harder than ~hat of the outer layer portion to increase the rigidity of blocks as a surface pattern in the outer layer portion of the tread, 2~ whereby the performances on snow in winter season, cornering stability and braking performance on ice are ~, ~ 3 ~
improved and the performances between summer season and winter season can be simultaneously established.
Further, the hardness of the expanded rubber in the outer layer portion of the tread is within a range of o~ 35~59, preferably 43~53. When the tread rubber is made softer, the true ground contact area of the tread can be increased to enhance the performances on ice, but the rigidity of the blocks in the tread is reduced to degrade the cornering stability on snow.
On the other hand, the reason why the first and second joint end parts are covered with the rubber reinforcing layer is due to the fact that a non-expanded skin layer of about 0.3 ~m in thickness is usually exi~tent in the outer surface of the expanded rubber and 1~ the boundary between the expanded rubber and the other rubber. Further, the expanded rubber is poor in the resistance to crack growth under a tension as compared with the ordinary rubber, so that crack is particularly apt to be caused from a side face of the block located in the shoulder of the tread. That is, in the conventional tread of the two-layer structure, the expanded rubber having a skin layer of about 0.3 ~m is existent in the vicinity of the shoulder being most liable to be subjected to cut damage and the like, resulting in the degradation of separation resistance and cut resistance from the side face of the tread.
1 3 ~
on the contrary, in the invention, the rubber reinforcing layer is arranged to cover the skin layer of the expanded rubber in the shoulder and the joint end parts, whereby the cut resistance and separation o~ resistance are improved in the vicinity of the shoulder.
The expanded rubber in the tread of the pneumatic tire according to the invention is formed by adding an expanding agent to the usual rubber composi-tion and curing them according to the usual tire building process. ~s the expandiny agent for the expanded rubber, use may be made, for example, of azodicarbon amide, dinitrosopentamethylene tetramine, azobisisobutyronitrile, benzene sulphonyl hydxazide, oxybis-benzene sulphonyl hydrazide, microcapsule of high 1~ boiling hydrocarbon resin and the like. Preferably, the sulphonyl hydrazide compounds, particularly oxybis-benzene sulp~onyl hydrazide are used in view of fine expansion.
The following examples are given in illustration 2~ f the invention and are not intended as limitations thereof. In these examples, the properties of the expanded rubber and tire performances were evaluated by the following test methods.
(1) Expansion ratio Vs The expansion ratio Vs of the expanded rubber was determined according to the aformentioned equation 1 3 ~
(2) after a block-like specimen was cut out from the expanded rubber layer in the tread of the test tire and the density Pl (g/orn ) of the specimen was measured and the density pO of non-expanded rubber (solid phase o~ rubber) of the tread was measured.
(2) Cell diameter and number of closed cells The cell diameter and number of closed cells in the expanded rubber were determined as follows. That is, a block-like specimen was cut out from the expanded rubber layer in the tread of the test tire and the cut surface of the specimen was photographed by means of an optical microscope with a magnification of 100~400, from which the cell diameter of the closed cell was measured.
Then, the number of cells having a cell diameter of not 1~ less than 5 ~m was measured over a total area of 4 mm2 or more, from which the number of closed cells per unit area of l mm2 was calculated.
(3) Flattening appearance (appearance of dynamic compression permanent deformation) ~fter two test tires were mounted onto a driving shaft of a passenger car having a displacement of l,500 cc and run on a general road over a distance of 20 r 000 km, the deformation quantity of each block in the block pattern of the tread was measured. The deforma-tion quantity of block was represented by a ratio (%) of displacement b of outer edge of the block in a certain - ~4-~3 ~
deformation direction to height a ranging from groove bottom of the block to outer surface of the block, wherein a case that the ratio b/a is 0~10% was ~, a case of 10~20% was l a case of 20~30% was ~ and a case of 05 more than 30% was x. The flattening phenomenon became larger and degraded in this order.
deformation direction to height a ranging from groove bottom of the block to outer surface of the block, wherein a case that the ratio b/a is 0~10% was ~, a case of 10~20% was l a case of 20~30% was ~ and a case of 05 more than 30% was x. The flattening phenomenon became larger and degraded in this order.
(4) Wear resistance After two test tires were mounted onto a driving shaft of a passenger car having a displacement of 1~ l,500 cc and run on concrete road surface of a test course at a given speed, the variation of groove depth was measured. The wear resistance was represented by an index on the basis that the comparative tire was lO0.
The larger the index value, the better the wear t 1~ resls ance.
The larger the index value, the better the wear t 1~ resls ance.
(5) Braking performance on ice After four test tires were attached to a passenger car having a displacement of l,500 cc, the braking distance was measured on ice at a temperature of -SC. The value was represented by an index when the comparative tire was 100. The smaller the index value, the better the braking performance.
(6) Change of hardness with lapse of time ~s to the ice-snow performances such as braking 2S performance on ice, hill climbing performance on snow and the like, the change of hardness of rubber block in ~3~a~
the surface portion of the tire was measured with the lapse of time. That is, after the tire was trained over a distance of 100 Icm, the hardness of the bloc~ (initial hardness Hd) was measured, and then the hardness after o~ the running over a distance of 5,000 km was measured.
Moreover, the measurement of the hardness was performed according to ~IS K6301, type A at 25C.
Then, the examples of the invention will be described with reference to the drawing.
(Examples 1~3, Comparative Examples 1~5) A single figure shows a first embodiment of the pneumatic tire according to the invention (Example 1).
As shown in the single figure, the pneumatic tire 1 (tire size: 165 SR13) comprises a tire casing 2, 1~ and a tread 3 covering a region between shoulders 4 of a crown portion 2a of the casing 2. The casing 2 comprises a pair of bead portions 5, a carcass portion 6 composed of a rubberized cord ply extending between the bead portions 5 and containing cords substantially arranged in the radial direction, and a belt portion 7 superimposed about a crown of the carcass portion 6 and arranged substantially in the circumferential direction of the tire. In the casing 2, sidewalls 8 are arranged on both outer sides of the carcass portion 6 in the axial direction of the tire.
The tread 3 consists of an outer layer portion :L 3 ~
3a contacting with ground surface and an inner layer portion 3b located inside the outer layer portion 3a.
The volume of the outer layer portion 3a is 60% of the total volume of the tread 3.
o~ In the vicinity of the tire shoul.der 4 are formed a first joint end part A of contact line between the outer layer portion 3a and the inner layer portion 3b in the clrcumferential direction of the tread 3 and a second joint end part B of contact line between the inner layer portion 3b and the sidewall 8 in the circumferential direction toward the bead portion.
A rubber reinforcing layer 10 of a triangular shape in section is a~ranged over a region ranging from each side face of the tread to the sidewall 8 to cover the first 1~ joint end part A and the second joint end part B as well as a part of side face of the outer layer portion 3a, a side face of the inner layer portion 3b and a part of side ~ace of the sidewall 8.
The outer layer portion 3a of the tread 3 is composed of an expanded rubber having a composition shown in the following Table 1. The hardness of the expanded rubber is 52. On the other hand, the i~ner layer portion 3b has a hardness Hd of 60 which is higher than that of the outer layer portion 3a and is composed 2~ of a rubber composition containing 80 parts by weight of carbon black and 15 parts by weight of oil based on ~ 3 ~
lO0 parts by weight of natural rubber and further containing usual additives. The sidewall 8 is a usual rubber having an excellent flexural resistance.
The rubber reinforc.ing layer 10 is a rubber having o~ excellent flexural resistance and cut reslstance.
Z~
~ 3 ~
__ _ _ _ _ _ _ ~0 ~ ~o, o In o Ln o t~ c~i o o ~
U ____ _ _ _ _ _ ~3~ o~ ~ o ~ o u~ o o o U __ _ _ _ _ _ ~3~ ~ ~o o ~ o ul o ~ ~ o o Ln b ~ ____ _ _ __ ~ ~ ~ O In U~ O U~ O O U~
_ , _ _ _ _ U~O O ~ O In O ~, O I~ In O O O
O O O O O O ~1 Ll~ O O N 11~ 1~1 O
U _ _ _ _ _ _ ~3~ o ~ ~ o o o o ~ ~ ~ o _ _ _ _ ~ _ ~ ~ ~r r~ o t~ o Ln co o o o r ~
U .4 t Z Z O ~- E tt5 = .C Z Z
~ t I 3 ~ ~ ~ ~ o ~ a o ~ t~ ~
S~ ~ ~ .,, ~ ta o c~ ~ ~ _ .,~s~ ~ ~ o ~1 tt5 ~ ta ~ æ z J~ tt5 ~) Q ~~rl N \~
ta ~ .~ c~ .~:: ,~ ,1 ....
O t~ s~ ~ ~: ~ .,~ 3 ~: ~ ~1 h ~ ~a ta ~ tt5 ~ ~:: ~ , ::5 ~ ~-,~ R ~i tl5 c) ~) 4~ tt5 ~: ~c #
~ ~ ~ ~ ~ ~ o a~ ~:: ~1 ~1 Q~
.~J t~ a) o ~ tt5 s~ ~ .,~ :~ :~
~ z; ~ ~ u~ U ~ cn ~ ~ u~ ~i ta ~ 3 ~
The above expanded rubber corresponds to a rubber composition (composition ~) as shown in ~able 1, i.e. a rubber composition containing 50 parts by weight o~ high reinEoraing carbon black NllO based on 100 parts 05 by weight o rubber component consisting of 60 parts by weight of natural rubber (glass transition temperature:
-72C) and 40 parts by weight of polybutadiene rubber (glass transition temperature: -100C) and containing no aromatic oil. This rubber composition further contains usual additives and an expanding agent (3 parts by weight of each of dinitrosopentamethylene tetramine and urea). Furthermore, the high reinorcing carbon black N110 has an N2SA of 143 m~/g. This rubber composition is built according to the usual tire manufacturing 1~ process and cured at a curing pressure index of 125 higher by 25% than the usual pressure in the curing, whereby closed cells 11 are formed.
The e~panded rubber (composition 4) used in the tire of Example 1 contains closed cells 11 at an expansion ratio Vs of 23% as shown in the following Table 2, wherein the number o~ closed cells having a cell diamPter of 5~30 ~m is 70% of total number of closed cells having a cell diameter of not less than 5 ~m per unit area as a whole of the expanded rubber.
The structure other than the tread 3 and the tire manuacturing method are the same as in the usual .~
~L 3 ~
pneumatic tire, so that the detalled description is omitted here.
Then, the test results on the performances of the pneumatic tires according to the invention will be 0~ described below.
By using each of the rubber compositions shown in Table 1, there are prepared 8 test tires (Examples 1~3, Comparative Examples 1~5). The tire of Example 1 is a tire shown in the single figure as previously 10 mentioned. In Examples 2 and 3 and Comparative Examples 1 to 5, the outer layer portion of the tread is formed by using the rubber composition shown in ~able 1 other than the composition 4. In Example 3, the number of closed cells having a cell diameter of 5~30 um is 90% of 1~ the total number of closed cells. In Comparative Example 1, the expanding agent is not used.
In Comparative Examples 2 and 3, the number of closed cells having a cell diameter of 5~30 ~um is less than 50 of the total number of closed cells. In Comparative 20 Example 4, the amount of carbon black is outside the range defined in ~he invention. In Comparative Example 5, the number of closed cells having a particular cell diameter is less than 50~ of the total number of closed cells and the closed cells having a cell diameter of not 2~ more than 5 ~um are existent.
AS the performances of the pneumatic tire, the braking performance on ice, flattening appearance, wear resistance and change of hardness of the expanded rubber during the running with the lapse of time were evaluated by the aforementioned test methods. The test results 06 are also shown in Table 2.
1~
.~
[~ ~ ~ ~ ` 5 ~ ~
~-r~ ~ ~rl ~ o Lnoo L O ~ ~ Ln ~ r~ o a~
. _ . _ _ I ~:
E ~ E 3 D Ln ~ o c~ ~) In Ln Ln .
~ I ~
E ~ E 3 Ln o N a~ O L Ll') Ln ~1 ~ __ _ I ~
ra ~31 r Ln ~ o oo O ~ Ln Ln c~ u~
_ _ I ~
N~ E ~ ~ E 3rr) o ~ ~ co <I L ~ Ln _ _ E~ I a) ~ I ~
0 D E E 1) N o N ~ __ X O O
~ r~ ~o r~ o l r~ O o Ln ~
~ VU~ .
U~~1 ~ ~ S~
P~1 ~C rl a~ aJ
o~ v~ ~ a~ ~ Q O
~_ .,, a~ s-- s-~ " a) ~s ~s X ~ U~ (~ 0-,1 S~ ~: O h Q) CJ
a~ ~ O 4~ -~ ~ ~ ~1 s~ ~:
s~ rcs s~ ,~ ~ s-~ ~ ~ s~ ~ 4~
as ~: o v ~:: d~ Q ~ -l s~ ., S ~1 O ~:
~ _ . ~ O ~ ~ ~s~ ~ ~ ~_~ ~Q ul 1 s~ s s~ a) u~ ~ ~, s_ s~ o as s~ s~ ~ ~ ~ ~ Y
s~ ~: O a~ ~ .,, ~ ~IS a~ .,, ~ ~ ~: s~
5- o ~: a) ~ O S~ ~ .~ h a~ ~ U as o s u~ p~,_ ~ ~ ~ ~ ~ c) ~ s~ ~ s~ .,~ s~ s~ o ~ o a~ ~ tn ~ O~o ~a as. ~ I s~ ~ ~ Q, a~ 1 s:: w 1 i~ ~ ~ o 3 Q as--s, s ~ m ~ ~ w ~ 3 ~ ~ o ~ S Q ~ Ln .,, I ~ a) ~ o o u~ ~ h o~ h o ~: a) ~ ~ o u~
~:) Ql rl S~ IS ~ ~1 aJ a) 1 ~3 S ~ O a) QI Q h t) h rl O ::~ ~rl X ~ O ~
?~ _ 1 4 ~) a~ h P~
i31~
As seen from Table 2, the braking performance on ice in the tires of Examples 1 to 3 are largely lmproved as compared with those of Comparative Examples 1 to 5.
Furthermorel in Examples 1 to 3, the flattening 05 appearance of the blocks after the running over a long period are largely improvedl and also the wear resistance is a sufficiently practicable level substantially equal to that of the conventional tire (Comparative Example 1). Moreoverl in the tires of 10 Examples 1 -to 3, there are caused no occurrence of damage in the vicinity of the tread shoulderl separation failure between the first and second joint end parts/
cut failure of the expanded rubber and side damage due to the chain or the likel so that the tire durabllity is 1~ considerably improved. And alsol the change of hardness in the tread after the running is considerably small as compared with those of Comparative Examples 1 to 5 As mentioned abovel according to the invention the outer layer portion of the tread is composed of an expanded rubber containing a particular rubber component and particular high reinforcing carbon black and oil and the number of closed cells having a particular cell diameter in the expanded rubber is restricted to a certain range of the total number of closed cells, 2~ whereby the flattening phenomenon can largely be reduced in use on ice and snow road surface over a long period l ~ L ~
of time and the braking performance on ice and snow road surface can considerably be improved. Furthermore, the wear reslstance is sufficient for practical use.
Moreover, the rubber reinforcing layer is OB arranged in the vicinity of the tread shoulder so as to cover the joint end part between outer and inner layer portions and joint end part between inner layer portion and sidewall, whereby the function of the tread is divided and the shoulder portion is reinforced and 10 consequently the ice-snow performances in winter season can be improved together with the performances in summer season and tire durability.
1~
2~
the surface portion of the tire was measured with the lapse of time. That is, after the tire was trained over a distance of 100 Icm, the hardness of the bloc~ (initial hardness Hd) was measured, and then the hardness after o~ the running over a distance of 5,000 km was measured.
Moreover, the measurement of the hardness was performed according to ~IS K6301, type A at 25C.
Then, the examples of the invention will be described with reference to the drawing.
(Examples 1~3, Comparative Examples 1~5) A single figure shows a first embodiment of the pneumatic tire according to the invention (Example 1).
As shown in the single figure, the pneumatic tire 1 (tire size: 165 SR13) comprises a tire casing 2, 1~ and a tread 3 covering a region between shoulders 4 of a crown portion 2a of the casing 2. The casing 2 comprises a pair of bead portions 5, a carcass portion 6 composed of a rubberized cord ply extending between the bead portions 5 and containing cords substantially arranged in the radial direction, and a belt portion 7 superimposed about a crown of the carcass portion 6 and arranged substantially in the circumferential direction of the tire. In the casing 2, sidewalls 8 are arranged on both outer sides of the carcass portion 6 in the axial direction of the tire.
The tread 3 consists of an outer layer portion :L 3 ~
3a contacting with ground surface and an inner layer portion 3b located inside the outer layer portion 3a.
The volume of the outer layer portion 3a is 60% of the total volume of the tread 3.
o~ In the vicinity of the tire shoul.der 4 are formed a first joint end part A of contact line between the outer layer portion 3a and the inner layer portion 3b in the clrcumferential direction of the tread 3 and a second joint end part B of contact line between the inner layer portion 3b and the sidewall 8 in the circumferential direction toward the bead portion.
A rubber reinforcing layer 10 of a triangular shape in section is a~ranged over a region ranging from each side face of the tread to the sidewall 8 to cover the first 1~ joint end part A and the second joint end part B as well as a part of side face of the outer layer portion 3a, a side face of the inner layer portion 3b and a part of side ~ace of the sidewall 8.
The outer layer portion 3a of the tread 3 is composed of an expanded rubber having a composition shown in the following Table 1. The hardness of the expanded rubber is 52. On the other hand, the i~ner layer portion 3b has a hardness Hd of 60 which is higher than that of the outer layer portion 3a and is composed 2~ of a rubber composition containing 80 parts by weight of carbon black and 15 parts by weight of oil based on ~ 3 ~
lO0 parts by weight of natural rubber and further containing usual additives. The sidewall 8 is a usual rubber having an excellent flexural resistance.
The rubber reinforc.ing layer 10 is a rubber having o~ excellent flexural resistance and cut reslstance.
Z~
~ 3 ~
__ _ _ _ _ _ _ ~0 ~ ~o, o In o Ln o t~ c~i o o ~
U ____ _ _ _ _ _ ~3~ o~ ~ o ~ o u~ o o o U __ _ _ _ _ _ ~3~ ~ ~o o ~ o ul o ~ ~ o o Ln b ~ ____ _ _ __ ~ ~ ~ O In U~ O U~ O O U~
_ , _ _ _ _ U~O O ~ O In O ~, O I~ In O O O
O O O O O O ~1 Ll~ O O N 11~ 1~1 O
U _ _ _ _ _ _ ~3~ o ~ ~ o o o o ~ ~ ~ o _ _ _ _ ~ _ ~ ~ ~r r~ o t~ o Ln co o o o r ~
U .4 t Z Z O ~- E tt5 = .C Z Z
~ t I 3 ~ ~ ~ ~ o ~ a o ~ t~ ~
S~ ~ ~ .,, ~ ta o c~ ~ ~ _ .,~s~ ~ ~ o ~1 tt5 ~ ta ~ æ z J~ tt5 ~) Q ~~rl N \~
ta ~ .~ c~ .~:: ,~ ,1 ....
O t~ s~ ~ ~: ~ .,~ 3 ~: ~ ~1 h ~ ~a ta ~ tt5 ~ ~:: ~ , ::5 ~ ~-,~ R ~i tl5 c) ~) 4~ tt5 ~: ~c #
~ ~ ~ ~ ~ ~ o a~ ~:: ~1 ~1 Q~
.~J t~ a) o ~ tt5 s~ ~ .,~ :~ :~
~ z; ~ ~ u~ U ~ cn ~ ~ u~ ~i ta ~ 3 ~
The above expanded rubber corresponds to a rubber composition (composition ~) as shown in ~able 1, i.e. a rubber composition containing 50 parts by weight o~ high reinEoraing carbon black NllO based on 100 parts 05 by weight o rubber component consisting of 60 parts by weight of natural rubber (glass transition temperature:
-72C) and 40 parts by weight of polybutadiene rubber (glass transition temperature: -100C) and containing no aromatic oil. This rubber composition further contains usual additives and an expanding agent (3 parts by weight of each of dinitrosopentamethylene tetramine and urea). Furthermore, the high reinorcing carbon black N110 has an N2SA of 143 m~/g. This rubber composition is built according to the usual tire manufacturing 1~ process and cured at a curing pressure index of 125 higher by 25% than the usual pressure in the curing, whereby closed cells 11 are formed.
The e~panded rubber (composition 4) used in the tire of Example 1 contains closed cells 11 at an expansion ratio Vs of 23% as shown in the following Table 2, wherein the number o~ closed cells having a cell diamPter of 5~30 ~m is 70% of total number of closed cells having a cell diameter of not less than 5 ~m per unit area as a whole of the expanded rubber.
The structure other than the tread 3 and the tire manuacturing method are the same as in the usual .~
~L 3 ~
pneumatic tire, so that the detalled description is omitted here.
Then, the test results on the performances of the pneumatic tires according to the invention will be 0~ described below.
By using each of the rubber compositions shown in Table 1, there are prepared 8 test tires (Examples 1~3, Comparative Examples 1~5). The tire of Example 1 is a tire shown in the single figure as previously 10 mentioned. In Examples 2 and 3 and Comparative Examples 1 to 5, the outer layer portion of the tread is formed by using the rubber composition shown in ~able 1 other than the composition 4. In Example 3, the number of closed cells having a cell diameter of 5~30 um is 90% of 1~ the total number of closed cells. In Comparative Example 1, the expanding agent is not used.
In Comparative Examples 2 and 3, the number of closed cells having a cell diameter of 5~30 ~um is less than 50 of the total number of closed cells. In Comparative 20 Example 4, the amount of carbon black is outside the range defined in ~he invention. In Comparative Example 5, the number of closed cells having a particular cell diameter is less than 50~ of the total number of closed cells and the closed cells having a cell diameter of not 2~ more than 5 ~um are existent.
AS the performances of the pneumatic tire, the braking performance on ice, flattening appearance, wear resistance and change of hardness of the expanded rubber during the running with the lapse of time were evaluated by the aforementioned test methods. The test results 06 are also shown in Table 2.
1~
.~
[~ ~ ~ ~ ` 5 ~ ~
~-r~ ~ ~rl ~ o Lnoo L O ~ ~ Ln ~ r~ o a~
. _ . _ _ I ~:
E ~ E 3 D Ln ~ o c~ ~) In Ln Ln .
~ I ~
E ~ E 3 Ln o N a~ O L Ll') Ln ~1 ~ __ _ I ~
ra ~31 r Ln ~ o oo O ~ Ln Ln c~ u~
_ _ I ~
N~ E ~ ~ E 3rr) o ~ ~ co <I L ~ Ln _ _ E~ I a) ~ I ~
0 D E E 1) N o N ~ __ X O O
~ r~ ~o r~ o l r~ O o Ln ~
~ VU~ .
U~~1 ~ ~ S~
P~1 ~C rl a~ aJ
o~ v~ ~ a~ ~ Q O
~_ .,, a~ s-- s-~ " a) ~s ~s X ~ U~ (~ 0-,1 S~ ~: O h Q) CJ
a~ ~ O 4~ -~ ~ ~ ~1 s~ ~:
s~ rcs s~ ,~ ~ s-~ ~ ~ s~ ~ 4~
as ~: o v ~:: d~ Q ~ -l s~ ., S ~1 O ~:
~ _ . ~ O ~ ~ ~s~ ~ ~ ~_~ ~Q ul 1 s~ s s~ a) u~ ~ ~, s_ s~ o as s~ s~ ~ ~ ~ ~ Y
s~ ~: O a~ ~ .,, ~ ~IS a~ .,, ~ ~ ~: s~
5- o ~: a) ~ O S~ ~ .~ h a~ ~ U as o s u~ p~,_ ~ ~ ~ ~ ~ c) ~ s~ ~ s~ .,~ s~ s~ o ~ o a~ ~ tn ~ O~o ~a as. ~ I s~ ~ ~ Q, a~ 1 s:: w 1 i~ ~ ~ o 3 Q as--s, s ~ m ~ ~ w ~ 3 ~ ~ o ~ S Q ~ Ln .,, I ~ a) ~ o o u~ ~ h o~ h o ~: a) ~ ~ o u~
~:) Ql rl S~ IS ~ ~1 aJ a) 1 ~3 S ~ O a) QI Q h t) h rl O ::~ ~rl X ~ O ~
?~ _ 1 4 ~) a~ h P~
i31~
As seen from Table 2, the braking performance on ice in the tires of Examples 1 to 3 are largely lmproved as compared with those of Comparative Examples 1 to 5.
Furthermorel in Examples 1 to 3, the flattening 05 appearance of the blocks after the running over a long period are largely improvedl and also the wear resistance is a sufficiently practicable level substantially equal to that of the conventional tire (Comparative Example 1). Moreoverl in the tires of 10 Examples 1 -to 3, there are caused no occurrence of damage in the vicinity of the tread shoulderl separation failure between the first and second joint end parts/
cut failure of the expanded rubber and side damage due to the chain or the likel so that the tire durabllity is 1~ considerably improved. And alsol the change of hardness in the tread after the running is considerably small as compared with those of Comparative Examples 1 to 5 As mentioned abovel according to the invention the outer layer portion of the tread is composed of an expanded rubber containing a particular rubber component and particular high reinforcing carbon black and oil and the number of closed cells having a particular cell diameter in the expanded rubber is restricted to a certain range of the total number of closed cells, 2~ whereby the flattening phenomenon can largely be reduced in use on ice and snow road surface over a long period l ~ L ~
of time and the braking performance on ice and snow road surface can considerably be improved. Furthermore, the wear reslstance is sufficient for practical use.
Moreover, the rubber reinforcing layer is OB arranged in the vicinity of the tread shoulder so as to cover the joint end part between outer and inner layer portions and joint end part between inner layer portion and sidewall, whereby the function of the tread is divided and the shoulder portion is reinforced and 10 consequently the ice-snow performances in winter season can be improved together with the performances in summer season and tire durability.
1~
2~
Claims (6)
1. A pneumatic tire comprising a tire casing and a tread covering a crown portion of said casing, charac-terized in that said tread is provided at its surface side with an expanded rubber layer in a volume corre-sponding to at least 10% of a total volume of said tread; and said expanded rubber layer is comprised of an expanded rubber containing not less than 50 parts by weight of at least one rubber component selected from natural rubber, polybutadiene rubber and styrene-butadiene copolymer rubber having a glass transition temperature of not higher than -45°C, a high reinforcing carbon black having an N2SA of 90~180 m2/g and not more than 20 parts by weight of an oil per 100 parts by weight of said rubber component; and said expanded rubber contains closed cells at an expansion ratio (Vs) of 5~50% so that the number of closed cells having a cell diameter of 5~30 µm is not less than 50% of total number of closed cells having a cell diameter of not less than 5 µm per unit area as a whole of said expanded rubber.
2. The pneumatic tire according to claim 1, wherein said tread consists of an outer layer portion comprised of the expanded rubber layer and an inner layer portion and is provided near to a shoulder thereof with a rubber reinforcing layer covering a first joint end part between the outer layer portion and the inner layer portion and a second joint end part between the inner layer portion and a sidewall portion.
3. The pneumatic tire according to claim 1, wherein said carbon black is added in an amount of 30 to 70 parts by weight based on 100 parts by weight of said rubber component.
4. The pneumatic tire according to claim 1, wherein said carbon black is carbon black ISAF or SAF.
5. The pneumatic tire according to claim 1, wherein said volume of the expanded rubber is 10~70% of the volume of the tread.
6. The pneumatic tire according to claim 2, wherein said outer layer portion has a hardness of 35°~59°.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP62220697A JP2661920B2 (en) | 1987-09-03 | 1987-09-03 | Pneumatic tire |
| JP220,697/87 | 1987-09-03 | ||
| JP275,338/87 | 1987-10-30 | ||
| JP62275338A JP2518870B2 (en) | 1987-10-30 | 1987-10-30 | Pneumatic tire |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1319091C true CA1319091C (en) | 1993-06-15 |
Family
ID=26523870
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000576198A Expired - Lifetime CA1319091C (en) | 1987-09-03 | 1988-08-31 | Pneumatic tires |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1319091C (en) |
| DE (1) | DE3829943A1 (en) |
| FR (1) | FR2620087B1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3360921B2 (en) * | 1994-03-25 | 2003-01-07 | 株式会社ブリヂストン | Pneumatic tire |
| EP1308319B1 (en) * | 2001-11-05 | 2009-07-22 | Continental Aktiengesellschaft | Pneumatic tire |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4249588A (en) * | 1978-04-27 | 1981-02-10 | The Goodyear Tire & Rubber Company | Pneumatic tire |
| JPS56110753A (en) * | 1980-02-08 | 1981-09-02 | Bridgestone Corp | Rubber composition for tire |
| JPS56163908A (en) * | 1980-05-23 | 1981-12-16 | Bridgestone Corp | Pneumatic tyre |
| JPS58402A (en) * | 1981-06-24 | 1983-01-05 | Toyo Tire & Rubber Co Ltd | Tire tread constitution with low rollability |
| JPS59206208A (en) * | 1983-05-09 | 1984-11-22 | Bridgestone Corp | Pneumatic tire suitable for ice-snow road |
| JPS6060008A (en) * | 1983-09-13 | 1985-04-06 | Toyo Tire & Rubber Co Ltd | All-weather type tiretread |
| DE3424732C1 (en) * | 1984-07-05 | 1985-11-21 | Hüls AG, 4370 Marl | Heat-vulcanizable treads for the production of treads for automotive pneumatic tires |
| JPS6218304A (en) * | 1985-07-17 | 1987-01-27 | Bridgestone Corp | Pneumatic tire |
| JPH0615637B2 (en) * | 1985-07-17 | 1994-03-02 | 東洋ゴム工業株式会社 | Rubber compounding composition for tire tread |
| DE3703480A1 (en) * | 1986-02-05 | 1987-08-06 | Bridgestone Corp | TIRE |
-
1988
- 1988-08-31 CA CA000576198A patent/CA1319091C/en not_active Expired - Lifetime
- 1988-09-02 DE DE19883829943 patent/DE3829943A1/en active Granted
- 1988-09-05 FR FR8811600A patent/FR2620087B1/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DE3829943C2 (en) | 1992-06-11 |
| FR2620087A1 (en) | 1989-03-10 |
| DE3829943A1 (en) | 1989-03-16 |
| FR2620087B1 (en) | 1994-10-21 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |
Effective date: 20100615 |