Resilient tires and wheels – Tires – resilient – Anti-skid devices
Reexamination Certificate
2001-02-01
2003-07-08
Johnstone, Adrienne C. (Department: 1733)
Resilient tires and wheels
Tires, resilient
Anti-skid devices
C152S458000
Reexamination Certificate
active
06588470
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a pneumatic tire improved in various tire performance parameters, which is effectively reinforced by incorporating a specific short fiber into a rubber member constituting the tire so as to satisfy the basic requirements for a tire.
As a means for reinforcing the rubber member constituting a tire, it has been a common practice to embed reinforcement cords in the rubber or to use a high-hardness rubber. When the rigidity of the rubber member was uniformly changed to improve a specific tire performance, however, a problem occurred that the other tire performance parameters were lowered.
With respect to a pneumatic radial tire, for example, it has been known that road noise can be reduced by enhancing the rigidity of the shoulder portions near the belt edges. It has therefore been a general practice to insert sheets or fillers made of a high hardness compound under both belt end portions to thereby enhance the rigidity of the shoulder portions. When such sheets or fillers made of a high-hardness compound are used, however, the basic performance parameters such as comfortableness in riding and stability in steering are changed by enhancement in the rigidity of the shoulder portions, even though road noise can be reduced.
Further, attempts have been made to enhance selectively the modulus of a rubber member constituting a tire in a specific direction by incorporating a short fiber made of nylon or the like into the rubber member and orienting it in the specific direction. However, the short fibers of the prior art have failed in attaining such effective reinforcement as to satisfy the basic requirements for a tire.
SUMMARY OF THE INVENTION
The first object of the present invention is to provide a pneumatic tire that is so effectively reinforced by incorporating a specific short fiber into a rubber member constituting the tire as to satisfy the basic requirements for a tire.
The second object of the present invention is to provide a pneumatic tire which is reduced in road noise by the use of the above specific short fiber with the basic performance parameters such as comfortableness in riding and stability in steering being kept at high levels.
The third object of the present invention is to provide a pneumatic tire which can exhibit excellent braking performance both on a dry road surface and on a wet road surface by virtue of the use of the above specific short fiber.
The fourth object of the present invention is to provide a pneumatic tire comprising an under tread made of a rubber exhibiting a small energy loss (for lowering rolling resistance), which tire has a reduced nonuniformity of gauge resulting from rubber flow occurring during the molding of the tire with vulcanization and improved stability in steering, by virtue of the use of the above specific short fiber.
The fifth object of the present invention is to provide a pneumatic tire that is reduced in the sidewall gauge by the use of the above specific short fiber with a reduction in the weight without impairing the resistance of the sidewall to external damage.
The sixth object of the present invention is to provide a pneumatic tire that is improved in durability by the use of the above specific short fiber with a decrease in the rubber volume of the bead portions.
The seventh object of the present invention is to provide a pneumatic tire which is reduced in the weight and improved in comfortableness in riding by the use of the above specific short fiber with the stability in steering being kept at a level equivalent or superior to that of a tire provided with steel reinforcements in the neighborhood of the bead fillers.
The pneumatic tire of the present invention achieving the above first object is one comprising a rubber member containing a short fiber (A′) formed by the fibrillation of a short fiber (A) whose cross section takes a sea-island structure essentially composed of at least two polymers.
When the above fibrillated short fiber (A′) is incorporated into the rubber member, the short fiber (A′) enhances the modulus of the member at low elongation by leaps and bounds to exhibit excellent reinforcing effect.
The term “modulus” used in this specification refers to “modulus at 20% elongation” (hereinafter referred to merely as “20% modulus”). A tire is generally used in the strain range of 50% or below, so that the characteristics of a rubber at low elongation based on 20% modulus highly correlate with tire performance parameters. Thus, a tire can be reinforced effectively by enhancing the 20% modulus. Accordingly, the reinforcement of a tire with the above short fiber makes it possible to improve various tire performance parameters required depending on the use of the tire.
Such 20% modulus can be determined according to the method of tensile test at low elongations as stipulated in JIS K6301. This method comprises using a test piece having a width of 5 mm, a length of 100 mm, a thickness of 2 mm and a distance of 40 mm between two gage marks, stretching this test piece preliminarily twice at a rate of 45±15 mm/min by 1.5 times the elongation (20%) to be subjected in the test, stretching the resulting test piece by 20% at the same rate as that employed in the preliminary stretching and keeping the same in the state thus stretched, and measuring the load after the lapse of 30 seconds. The modulus at 20% elongation (20% modulus) can be determined by the following formula. The measurement of the load is repeated generally four times and the average of the four values is used.
&sgr;
20
=F
20
/S
&sgr;
20
: modulus at 20% elongation (MPa)
F
20
: load at 20% elongation (N)
S: sectional area of test piece
A pneumatic tire of the present invention achieving the above second object is a pneumatic radial tire which comprises a carcass layer bridging a pair of, i.e., lefthand and righthand bead portions and a plurality of belt layers lying in the tread portion on the outside of the carcass layer and which further comprises compound sheets lying in both tire widthwise end portions of the belt layers respectively, with the ratio of the tire circumferential modulus (b) of the compound sheets to the tire radial modulus (a) thereof (i.e., b/a ratio) being adjusted to 1.2 or above by incorporating a short fiber (A′) formed by the fibrillation of a short fiber (A) whose cross section takes a sea-island structure essentially composed of at least two polymers into the rubber constituting the compound sheets in a proportion of 0.5 to 15 parts by weight per 100 parts by weight of the rubber and orienting the fibrillated short fiber (A′) in a tire circumferential direction.
Another pneumatic tire of the present invention achieving the above second object is a pneumatic radial tire which comprises a carcass layer bridging a pair of, i.e., lefthand and righthand bead portions and a plurality of belt layers lying in the tread portion on the outside of the carcass layer and which further comprises compound sheets lying in both tire widthwise end portions of the belt layers respectively, with the ratio of the tire circumferential modulus (b) of the compound sheets to the tire radial modulus (a) thereof (i.e., b/a ratio) being adjusted to 1.2 or above by incorporating a short fiber (A′) formed by the fibrillation of a short fiber (A) whose cross section takes a sea-island structure essentially composed of at least two polymers and a composition comprising a short fiber (B) made of a thermoplastic polymer having amido groups in the main chain and a matrix made of a rubber and/or a polyolefin wherein the short fiber (B) is dispersed in the matrix and chemically bonded to the matrix into the rubber constituting the compound sheets in proportions of 0.5 to 10 parts by weight of the fibrillated short fiber (A′) and 1 to 15 parts by weight of the short fiber (B) per 100 parts by weight of the rubber and orienting the fibrillated short fiber (A′) and the short fiber (B) in a tire circumferential direction.
In the above cases wher
Kanenari Daisuke
Mama Riichiro
Yamakawa Kazuto
Johnstone Adrienne C.
The Yokohama Rubber Co. Ltd.
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