Patent Application
20170197480
The present application is based on, and claims priority from, Japanese Application No. JP2016-004821 filed Jan. 13, 2016, the disclosure of which is hereby incorporated by reference herein in its entirety.
The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire (hereinafter, also simply referred to a “tire”) in which the conductivity is improved.
In recent years, with increasing demand for fuel-efficiency of tires, rubber members of tires have been becoming low-loss. However, when a larger amount of silica is added in place of carbon black or when the amount of carbon black is reduced by increasing the particle size of the carbon black in order to make rubber for tires low-loss, the electric resistance value of the rubber increases. Accordingly, when the whole rubber composition to be used for a tire is made low-loss, the electric resistance of the tire increases, which leads to radio noise, generation of static electricity before opening/closing a door of a vehicle, or the like, and therefore, a technique for reducing the electric resistance of a tire is demanded.
To address the above problems, conventionally, a variety of attempts for reducing the electric resistance of a tire by arranging conductive fibers have been made. For example, Japanese Unexamined Patent Application Publication No. H3-169711 discloses an electrically conductive tire in which carcass cords of a carcass ply nearest to a breaker among carcass plies and breaker cords are each formed by an assembly composed of at least one metal filament and a large number of organic fibers, as an electrically conductive tire which can ground static electricity generated on a vehicle body smoothly on a road surface.
As described above, conventionally, a large number of attempts for reducing the electric resistance of a tire have been made unsatisfactorily. For example, as in the above-described Japanese Unexamined Patent Application Publication No. H3-169711, when a metal fiber is used for a carcass cord, there arise problems such as decrease in durability and considerable deterioration in productivity due to application of an inelastic fiber. Establishment of a technique capable of reducing the electric resistance of a tire without greatly changing a variety of performances or manufacturing processes required for the tire has thus been demanded.
Accordingly, an object of the present invention is to solve the above-described problems and to provide a pneumatic tire in which the electric resistance is reduced without adversely affecting other performances or manufacturing processes.
The present inventor intensively studied to find that the conductivity of a tire can be improved by arranging a composite fiber containing a conductive fiber and a non-conductive fiber inside the tire. The present inventor also found that it is important to expose the composite fiber on both surfaces of a carcass ply in order to secure a conductive path inside the tire, thereby completing the present invention. Herein, the composite fiber refers to a fiber composed of a plurality of different kinds of fibers.
That is, the present invention is a pneumatic tire comprising a carcass as a skeletal structure composed of at least one carcass ply extending toroidally between a pair of bead portions, at least one layer of a belt located on the outer side of the carcass in the tire radial direction of the crown portion, characterized in that
the tire is provided with a cushion rubber and a tread rubber forming a tread portion in turn on the outer side of the belt in the tire radial direction, and
a composite fiber containing a conductive fiber and a non-conductive fiber is extended at least from a pair of the bead portions to portions in contact with the cushion rubber or a pair of belt under cushions arranged at the outer ends of the belt in the tire width direction, so as to expose the composite fiber to both surfaces of the carcass at the outer and inner sides of the tire.
In the present invention, preferably, the non-conductive fiber is made of an organic material and the composite fiber contains not less than 50% by mass of the non-conductive fiber. In the present invention, preferably, the composite fiber is sewn to the carcass. In this case, suitably, the sewing pitch of the composite fiber is from 2 to 40 mm. Herein, the sewing pitch refers to a distance corresponding to one stitch when a composite fiber is sewn to a carcass, and corresponds to a in the following
Still further, in the tire according to the present invention, it is possible that a bleeder cord is extended at least from the pair of bead portions to portions in contact with the cushion rubber or the belt under cushion, and the composite fiber is arranged in place of 3 to 100% by mass of the bleeder cord.
Still further, in the present invention, preferably, the composite fiber is composed of spun yarns, and suitably, the fineness of the composite fiber is from 20 to 1,000 dtex. Still further, preferably, the composite fiber is arranged at an angle of 30 to 150° with respect to the tire circumferential direction, and more preferably, the composite fiber is arranged at an angle of 50 to 130° with respect to the tire circumferential direction. Still more preferably, the composite fiber is arranged at an angle of 80 to 100° with respect to the tire circumferential direction.
Still further, in the present invention, preferably, the conductive fiber contains at least one of a metal-containing fiber, a carbon-containing fiber, and a metal oxide-containing fiber, and also preferably, the non-conductive fiber contains at least one of cotton, nylon, polyester, and polypropylene. Still further, in the present invention, suitably, the breaking elongation Eb of the composite fiber is not less than 5%. Preferably, the resistance value of the composite fiber is not larger than 1.0×107 Ω/cm, and more preferably, the resistance value of the composite fiber is not larger than 1.0×103 Ω/cm. Still further, in the present invention, preferably, a conductive rubber portion is provided from a tread grounding portion to the outer surface of the cushion rubber in the tire radial direction.
According to the present invention, it becomes possible to realize a pneumatic tire whose electric resistance is reduced without adversely affecting other performances or manufacturing processes.
Hereinafter, embodiments according to the present invention will be described in detail with reference to the Drawings.
In the present invention, it is important that a composite fiber 3 containing a conductive fiber and a non-conductive fiber is extended at least from the pair of bead portions 11 to portions in contact with the cushion rubber 13C or a belt under cushion 14 arranged at the outer ends of the belt layer in the tire width direction. The composite fiber 3 is arranged so as to be exposed to both surfaces of the carcass 1 at the outer and inner sides of the tire. By arranging the composite fiber 3 in the above-described manner, a conductive path inside the tire can be secured, and the electric resistance of the tire can be reduced. That is, in the present invention, since the composite fiber 3 containing a conductive fiber is arranged so as to be exposed to both surfaces of the carcass 1 at the outer and inner sides of the tire, a portion where the composite fiber is exposed to the tire outer side surface can secure an electrical connection with a tire grounding portion, and at the same time, a portion where the composite fiber is exposed to the tire inner side surface can secure an electrical connection with a rim 20 via the rubber chafer 4 made of a conductive rubber at a turn-up portion 1B, whereby a conductive path inside the tire can be secured.
In the present invention, since the composite fiber 3 contains a conductive fiber and a non-conductive fiber, elongation of the composite fiber can be secured to some extent different from a conventional metal fiber or a carbon fiber, and therefore, the composite fiber does not break when a stress is loaded during a tire manufacturing process or when a strain is applied to the tire during traveling of a vehicle. Further, in the present invention, since the composite fiber 3 is not one which is arranged in place of a skeleton member such as a carcass ply, a problem such as deterioration in durability of a tire is not caused. Therefore, according to the present invention, since the electric resistance can be reduced without adversely affecting other performances or manufacturing processes, a pneumatic tire without problems due to increase in electric resistance can be realized even when a reduction in fuel consumption is attempted by making a tire rubber member low-loss.
The composite fiber 3 according to the present invention may contain a conductive fiber and a non-conductive fiber. Specific examples of the conductive fiber include a metal-containing fiber, a carbon-containing fiber, and, a metal oxide-containing fiber. At least one of these fibers can be used. Herein, a metal-containing fiber refers to a fiber whose content of metal is from 5 to 100% by mass, and examples of metal and metal oxide include stainless steel, steel, aluminum, copper, and oxidation thereof. Examples of a non-conductive fiber include an organic material such as cotton, nylon, polyester such as polyethylene terephthalate, and polypropylene. At least one of these can be used. A composite fiber composed of such a conductive fiber and non-conductive fiber has a favorable elongation and excellent adhesion, which is preferable.
The ratio of a conductive fiber to a non-conductive in the composite fiber 3 used in the present invention is not particularly limited. Suitably, 50% by mass, for example, 80 to 98% by mass of a non-conductive fiber is contained in the composite fiber. When the composite fiber 3 contains a non-conductive fiber at the above-described ratio, elongation of the composite fiber can be favorably secured, which is preferable.
Specific examples of the composite fiber 3 in the present invention include Bekinox (Bekinox, registered trademark) manufactured by Bekaert Corporation and Clacarbo (registered trademark) KC-500R and KC-793R manufactured by kuraray trading Co., Ltd.
From the viewpoint of attaining air bleeding property, conductivity, and durability at the same time, the fineness of the composite fiber 3 is preferably from 20 to 1,000 dtex, and more preferably from 150 to 600 dtex.
The breaking elongation Eb of the composite fiber 3 is preferably not less than 5% since breakage during manufacturing can be suppressed, and more preferably, the breaking elongation is not less than 6% since the composite fiber is less likely to break even when an abnormal input is applied to the composite fiber during using a tire. The breaking elongation Eb can be, for example, from 5 to 15%. Here, the breaking elongation Eb of the composite fiber 3 can be measured at 23° C. in accordance with a method of measuring “elongation at break” defined in JIS K 6251:2010.
The resistance value of the composite fiber 3 is suitably not less than 1.0×107 Ω/cm, more suitably not less than 1.0×103 Ω/cm, and further suitably from 10 to 1.0×103 Ω/cm. From the viewpoint of surely securing conductive path, the resistance value of the composite fiber 3 is preferably in the above-described range.
In the present invention, the composite fiber 3 needs to be extended at least from the bead portion 11 to a portion in contact with the cushion rubber 13C or belt under cushion 14, and preferably, as illustrated, the composite fiber 3 is extended from the bead portion 11 to the tread portion 13. Since a conductive rubber is usually used for the cushion rubber 13C and belt under cushion 14, a conductive path can be secured by arranging the composite fiber 3 at least from the bead portion 11 to a portion in contact with the cushion rubber 13C or belt under cushion 14. Since a conductive path from the cushion rubber 13C to a tread grounding portion is secured by a conductive rubber portion 5 which is usually provided near the tire equator line CL, from the viewpoint of reducing the length of the conductive path, the composite fiber 3 is preferably extended from the bead portion 11 to the tread portion 13. Here, in the present invention, the cushion rubber 13C is a rubber member located between a tread rubber 13G and a coating rubber of the belt layer 2 (when a cap layer is provided, a coating rubber of the cap layer) at least on the tire equator line CL, and is a rubber member which is usually extended to near a tire shoulder portion and is not exposed to the tire outer surface since the rubber member is covered by the tread rubber 13G and, depending on a state of arrangement of rubbers, a sidewall rubber.
The belt under cushion 14 is a conductive rubber member provided at the outer ends of the belt layer 2 in the tire width direction, and, as illustrated, is in contact with the cushion rubber 13C and positioned on the inner side thereof in the tire radial direction. More specifically, the belt under cushion 14 is a conductive rubber member which is arranged, in the vicinity of the outer end in the tire width direction of the belt member including a plurality of layers of belt layers and a covering rubber of a belt cord, on the inner side of the tire radial direction of at least one belt layer, in particular, all the belt layers, and is arranged on the outer side of the carcass 1 in the tire radial direction. The cushioning property of a portion where the belt under cushion 14 is arranged can be improved.
In the present invention, the arrangement positions of ends of the cushion rubber 13C and the belt under cushion 14 in the tire width direction can be appropriately determined in relation to other members. For example, in
In the Embodiments illustrated in
Here, as illustrated, the conductive rubber portion 5 can be provided from the tread grounding portion to the outer surface of the cushion rubber 13C in the tire radial direction all around the tire in the tire circumferential direction. That is, the conductive rubber portion 5 is provided so as to penetrate the tread rubber 13G from the tread grounding portion.
In the present invention, the composite fiber 3 needs to be arranged so as to be exposed to both surfaces of the carcass 1 at the outer and inner sides of the tire.
In this case, a sewing pitch of the composite fiber 3 can be usually from 2 to 40 mm, and particularly from 5 to 25 mm along the extending direction of the composite fiber 3. From the viewpoint of more surely securing a conductive path, this rage is preferable.
As illustrated in
Further, as illustrated in
As illustrated in
Still further, as a modified example of
Still further, as a modified example of
In the present invention, from the viewpoint of manufacturability, a state of arrangements illustrated in
In this case, the winding pitch of the composite fiber 3 can be usually 1 to 12/m, in particular, 2 to 5/m along a longitudinal direction of the carcass treatment 21, i.e., a direction orthogonal to the extending direction of the carcass ply cord. From the viewpoint of surely securing a conductive path, this range is preferable.
In the present invention, the composite fiber 3 may be arranged so as to be exposed to both surfaces of the carcass 1 at the outer and inner sides of the tire. A conductive path can be secured when a portion where the composite fiber is exposed to the tire outer side and a portion where the composite fiber is exposed to the tire inner side are electrically connected with each other at least one location. Herein, that a portion where the composite fiber 3 is exposed to the tire outer side and a portion where the composite fiber is exposed to the tire inner side are electrically connected with each other does not necessarily mean that they are physically connected with each other.
Although depending on the resistance value of the composite fiber 3, from the viewpoint of surely securing a conductive path in the tire circumferential direction, the composite fiber 3 is preferably arranged at an end count of not less than 0.04/5 cm, more preferably at an end count of not less than 0.1/5 cm, and for example at an end count of from 0.1 to 0.2/5 cm.
Still further, the composite fiber 3 is preferably arranged at an angle of from 30 to 150° with respect to the tire circumferential direction, more preferably at an angle of from 50 to 130°, and further preferably at an angle of from 80 to 100°. When the extending direction of the composite fiber 3 is too close to the tire circumferential direction, the length of a conductive path is large, which is not preferable. The composite fiber 3 is not always arranged linearly as illustrated in
In the present invention, the composite fiber 3 can be arranged in place of a bleeder cord which has been conventionally arranged for bleeding air in a carcass ply during vulcanization. A bleeder cord is a cord member which is arranged on one side or both sides of a carcass or a belt layer in order to reduce air inclusion failures occurring during a tire production process, and which is generally composed of a cotton yarn, a polyester yarn, or the like. A bleeder cord can reduce air inclusion failures by absorbing or passing air included in a tire during a tire production process. Since a bleeder cord is usually extended at least from the bead portion 11 to a portion which is in contact with a cushion rubber 13C or belt under cushion 14, an effect due to the arrangement of the composite fiber 3 can be obtained without adding a new member by replacing a portion of or whole of the bleeder cord with the composite fiber 3. As a matter of course, an expected effect of the present invention can be obtained by leaving the bleeder cord as it is and adding the composite fiber 3 thereto.
When the composite fiber 3 is arranged in place of a conventional bleeder cord, the composite fiber 3 can be arranged in place of 3 to 100% by mass, and suitably 20 to 50% by mass of the bleeder cord. When an equivalent number of composite fibers 3 are replaced with, an expected effect according to the present invention can be surely obtained.
The composite fiber 3 which is used in the present invention may be a pun yarn or a filament yarn, and suitably is a spun yarn (blended yarn) obtained by spinning a short fiber. In order to secure the adhesive property of the composite fiber 3 with rubber, the composite fiber 3 needs to be subjected to a dipping process using an adhesive for securing adhesion between an organic fiber and rubber. However, when an adhesive surface coating is provided on the composite fiber 3 by the dipping process, air bleeding properties via the composite fiber 3 deteriorate. For this reason, when the composite fiber 3 is arranged in place of the bleeder cord, it is preferable that only a portion of the dipping process is performed, and it is more preferable that the dipping process is not performed. However, when the composite fiber 3 has no adhesive surface coating, adhesion between the composite fiber 3 and un-vulcanized rubber decreases and the composite fiber 3 may be dropped during manufacturing. In this case, by using a spun yarn (blended yarn), adhesion with rubber can be secured by anchoring effect of a short fiber even without a dipping process, and air bleeding properties are also maintained, which is preferable. When a filament yarn is used, the filament yarn is preferably twisted in order to maintain air bleeding properties. In this case, the twist count is suitably not less than 10/10 cm, and may be, for example, 30 to 60/10 cm.
On the other hand, when a portion of the bleeder cord is replaced with the composite fiber 3, air bleeding properties can be secured by remaining bleeder cords composed, for example, of a cotton yarn, and therefore, both adhesion with rubber and air bleeding properties can be attained at the same time even when the composite fiber 3 is subjected to a dipping process. Accordingly, in the present invention, although the composite fiber 3 may be subjected to a dipping process, from the viewpoint of securing the degree of freedom of the design such as replacing all the bleeder cords with the composite fiber 3, it is preferable that the composite fiber is not subjected to a dipping process.
In the present invention, only that the above-described composite fiber 3 is arranged is important, and by this, an expected effect of the present invention can be obtained. Other portions of the tire structure can be appropriately configured in accordance with an ordinary method, and are not particularly restricted.
For example, in the present invention, since the electric resistance of a tire can be reduced by the arrangement of the composite fiber 3, a rubber composition which is made more low-loss than that of a conventional tire structure can be used as a tire case member such as a coating rubber for a carcass ply, thereby improving the low fuel consumption of the tire.
In the illustrated tire, the carcass 1 is turned up around the bead core 6 and curled up to the outer side in the tire radial direction to form the turn-up portion 1B, and a bead filler 7 with a tapered cross-section is arranged on the outer side of the bead core 6 in the tire radial direction. Further, although not illustrated, the tire according to the present invention can be provided with at least one cap layer covering whole the belt layer 6 or at least one layered layer covering only the end of the belt layer 6 on the outer side of the belt layer 6 in the tire radial direction, as needed. Still further, although not illustrated, an inner liner is usually provided on the innermost surface of the tire.
The present invention will be described in more detail using Examples.
A pneumatic tire with a tire size of 195/65R15 comprising a carcass as a skeletal structure composed of one carcass ply extending toroidally between a pair of bead portions and two belt layers located on the outer side of the carcass in the tire radial direction of the crown portion was manufactured. A bleeder cord (material: cotton) and a fiber material listed on Tables 1 to 5 below were arranged on the tire from a bead portion to a tread portion so as to be exposed to both surfaces of the carcass at the outer and inner sides of the tire.
The bleeder cord was arranged on the outer surface of the carcass at an angle of 90° with respect to the tire circumferential direction. As illustrated in
For each of the obtained test tire, the manufacturability, the air inclusion occurrence rate, and the electric resistance value were evaluated. The results thereof are listed on the Table below.
The manufacturability of each test tire was evaluated as “OK” when there was no breakage of a yarn during normal manufacturing, and evaluated as “NG” when there was breakage of a yarn during normal manufacturing.
The air inclusion occurrence rate of each test tire was evaluated according to the following manner. The air inclusion occurrence rate can be said to be favorable when it is less than 1%.
In accordance with the above-described method, 100 tires were manufactured. The number of the products in which an air inclusion was occurred was counted, and the ratio of the counted number to 100 was calculated as the air inclusion occurrence rate.
As illustrated in
The lower the electric resistance value of the tire, the better.
As listed on the above-described Tables, it was confirmed that the electric resistance of a test tire of each Example in which a composite fiber containing a conductive fiber and a non-conductive fiber was extended from a bead portion to a portion in contact with a cushion rubber so as to be exposed to both surfaces of the carcass at the outer and inner sides of the tire was reduced without adversely affecting air bleeding properties or a manufacturing process.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-004821 | Jan 2016 | JP | national |
