Patent Description:
Conventionally, a pneumatic tire in which a sound absorbing material in the form of a sponge has been fixed on a tire inner cavity side of a tread portion in order to reduce noise generated from the tire during running of a vehicle, has been proposed (see <CIT>).

In addition, a pneumatic tire including, on a tire inner cavity side of a tread portion thereof, a sealant layer and a sound absorbing material fixed to the sealant layer in order to improve both the noise performance and the puncture sealing performance of the tire, has been proposed in recent years (see <CIT>). This type of pneumatic tire is expected to exhibit the following advantageous effect. For example, when a through-hole is formed in the tread portion owing to nail treading or the like, a part of the sealant layer flows into the through-hole so as to achieve sealing thereof so that the air sealing performance of the tire is ensured.

<CIT> discloses a tire according to the preamble of both claims <NUM> and <NUM>. Another related tire is disclosed in <CIT>.

The pneumatic tire in which the sound absorbing material is fixed on the sealant layer has the problem that the weight of the tire increases.

The present invention has been made in view of the above problem, and a main object of the present invention is to provide a pneumatic tire that can suppress increase in the weight of the tire while maintaining air sealing performance.

The present invention is directed to a pneumatic tire having the features of independent claim <NUM>. Furthermore, the present invention is directed to a pneumatic tire having the features of independent claim <NUM>.

The pneumatic tire according to the present invention can suppress increase in the weight of the tire while maintaining air sealing performance, by employing the above configuration.

It should be understood that the drawings contain exaggerated expressions and expressions that differ from the dimensional ratio of the actual structure in order to help the understanding of the present invention. In addition, the same or common elements are denoted by the same reference characters throughout each embodiment, and redundant descriptions thereof are omitted. Furthermore, the specific configurations shown in the embodiment and the drawings are for understanding the contents of the present invention, and the present invention is not limited to the specific configurations shown.

<FIG> is a cross-sectional view of a pneumatic tire <NUM> according to the present embodiment. In the cross-sectional view, the pneumatic tire <NUM> is in a normal state. The normal state of the pneumatic tire <NUM> refers to a state for uniquely determining the posture of the pneumatic tire <NUM> and is a state where: the pneumatic tire <NUM> is mounted to a normal rim R under a normal internal pressure; and no load is applied to the pneumatic tire <NUM>. Hereinafter, it is understood that, in the present description, dimensions and the like of each component of the pneumatic tire <NUM> are values measured in the normal state, unless otherwise specified.

In the present description, the "normal rim" refers to a rim having a rim width that is suitable for effectively exhibiting performances of the pneumatic tire <NUM>. Specifically, the "normal rim" is the "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, or the "Measuring Rim" in the ETRTO standard. In this manner, the "normal rim" can be defined for each standard on which the pneumatic tire <NUM> is based.

In the present description, the "normal internal pressure" refers to an air pressure that is defined, in a standard system including a standard on which the pneumatic tire <NUM> is based, by the standard for each tire. The "normal internal pressure" is the maximum air pressure in the JATMA standard, the maximum value indicated in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, or the "INFLATION PRESSURE" in the ETRTO standard.

As shown in <FIG>, the pneumatic tire <NUM> according to the present embodiment is, for example, a tubeless tire having a radial structure. The pneumatic tire <NUM> is formed in, for example, a toroidal shape so as to include a tread portion <NUM>, a pair of sidewall portions <NUM>, and a pair of bead portions <NUM>. The pair of bead portions <NUM> include respective non-stretchable bead cores <NUM> embedded therein.

The pneumatic tire <NUM> includes, for example, a carcass <NUM> extending on and between the bead cores <NUM>, a belt layer <NUM> disposed inward of the tread portion <NUM> and outward of the carcass <NUM> in a tire radial direction, and a tread rubber <NUM> disposed outward of the belt layer <NUM>. These elements can be provided as appropriate according to a conventional manner. In addition, a band layer (not shown) including a reinforcing cord extending in a tire circumferential direction, or the like may be disposed as necessary between the belt layer <NUM> and the tread rubber <NUM>.

On a tire inner cavity i side of the carcass <NUM>, an inner liner layer <NUM> is disposed over substantially the entire region thereof. The inner liner layer <NUM> is made from an air-impermeable rubber such as isobutylene-isoprene rubber and prevents air in the tire inner cavity i from leaking to outside as a result of permeation.

The pneumatic tire <NUM> according to the present embodiment includes, on the tire inner cavity i side of the tread portion <NUM>, a self-sealing sealant layer <NUM> and a sound absorbing material <NUM>, in the form of a sponge, fixed to the sealant layer <NUM>.

The sound absorbing material <NUM> is fixed to the inner side in the tire radial direction of the sealant layer <NUM> and exposed to the tire inner cavity i. In the present embodiment, an outer surface 12a in the tire radial direction of the sound absorbing material <NUM> is in direct contact with the sealant layer <NUM>, thereby being held by the sealant layer <NUM> owing to the adhesiveness of the sealant layer <NUM>.

The sound absorbing material <NUM> in the present embodiment is formed of a soft sponge resulting from foaming a rubber or a synthetic resin. A porous portion on the surface of the sponge converts the vibrational energy of the air in the tire inner cavity i into thermal energy. Therefore, the sound absorbing material <NUM> can reduce resonance noise and the like during running with the tire.

The sound absorbing material <NUM> in the present embodiment is formed of a sponge having a closed cell structure. In the sound absorbing material <NUM> having a closed cell structure, a plurality of air bubbles separately exist in a state of being disconnected from one another. Such a sound absorbing material <NUM> does not allow a sealant agent forming the sealant layer <NUM> to permeate the inside thereof, and thus the performance of the sealant layer <NUM> is not decreased. In addition, the sound absorbing material <NUM> having a closed cell structure is expected to exhibit the following additional advantageous effect. That is, upon contact with a nail, a part of the sound absorbing material <NUM> is fractured, and fragments thereof enter the resultant through-hole alone or together with the sealant agent, thereby sealing the through-hole. Therefore, the sound absorbing material <NUM> in the present embodiment contributes to supplementing the air sealing performance.

The sound absorbing material <NUM> in the present embodiment is configured by, for example, disposing a belt-shaped sponge having a rectangular cross-sectional shape, in a substantially annular shape along the tire circumferential direction. In a preferable mode, both end portions in the tire circumferential direction of the sound absorbing material <NUM> are brought into contact with each other or are apart from each other at a short interval. In another mode, a plurality of the sound absorbing materials <NUM> may be provided intermittently in the tire circumferential direction.

The position, the shape, the size, and the like of the sound absorbing material <NUM> are not particularly limited, and the shape and the size thereof only have to be determined as appropriate so as to enable reduction of noise during running with the tire. The sound absorbing material <NUM> in <FIG> is disposed substantially at the center position in a tire axial direction of the tread portion <NUM>. In the tire cross section shown in <FIG>, the cross-sectional area of the sound absorbing material <NUM> is preferably about <NUM>% to <NUM>% of the area of the tire inner cavity i enclosed by the pneumatic tire <NUM> and the normal rim R.

The material of the sound absorbing material <NUM> is not particularly limited, but, for example, a polyurethane sponge and the like having excellent weather resistances are suitable. In particular, an ether/ester-based mixed polyurethane sponge is desirable.

The density of the sound absorbing material <NUM> is not particularly limited. However, for exhibition of a more excellent road noise absorbing effect, the density is, for example, preferably not higher than <NUM>/m<NUM>, more preferably not higher than <NUM>/m<NUM>, and further preferably not higher than <NUM>/m<NUM>. Meanwhile, regarding the lower limit of the density of the sound absorbing material <NUM>, the density is, for example, preferably not lower than <NUM>/m<NUM>, more preferably not lower than <NUM>/m<NUM>, and further preferably not lower than <NUM>/m<NUM> from the viewpoint of durability and the like.

The hardness of the sound absorbing material <NUM> is not particularly limited. However, if the hardness of the sound absorbing material <NUM> is low, a foreign object such as a nail is more likely to pierce the sound absorbing material <NUM> upon contact with the foreign object. From such a viewpoint, the hardness of the sound absorbing material <NUM> is, for example, preferably not lower than <NUM> (N/<NUM><NUM>). Meanwhile, if the hardness of the sound absorbing material <NUM> is excessively high, the noise reduction effect might relatively decrease. From such a viewpoint, the hardness of the sound absorbing material <NUM> is, for example, preferably not higher than <NUM> (N/<NUM><NUM>). In the present description, the hardness of the sound absorbing material <NUM> is defined as a hardness measured according to Method D for the hardness test in JIS K6400-<NUM> (<NUM>).

The elongation of the sound absorbing material <NUM> is not particularly limited. However, if the elongation of the sound absorbing material <NUM> is high, elastic deformation is likely to be accelerated upon contact with a foreign object so that piercing by the foreign object is further suppressed. From such a viewpoint, the elongation of the sound absorbing material <NUM> is, for example, preferably not lower than <NUM>% and more preferably not lower than <NUM>%. Meanwhile, the elongation of the sound absorbing material <NUM> is, for example, preferably not higher than <NUM>% and more preferably not higher than <NUM>% from the viewpoint of, for example, ease of material obtainment and the like. In the present description, the elongation of the sound absorbing material <NUM> is defined as an elongation that complies with JIS K6400-<NUM> (<NUM>) and that is obtained at break of a test piece.

The tensile strength of the sound absorbing material <NUM> is not particularly limited, but is, for example, preferably not lower than <NUM> kPa from the viewpoint of suppressing, for example, damage upon nail treading. Meanwhile, the tensile strength of the sound absorbing material <NUM> is, for example, preferably not higher than <NUM> kPa from the viewpoint of cost, productivity, ease of obtainment in the market, and the like for the sound absorbing material <NUM>.

The sealant layer <NUM> is disposed on the tire inner cavity i side of the tread portion <NUM>, i.e., on the further inner side of the tire relative to the inner liner layer <NUM>. The sealant layer <NUM> in the present embodiment is made from a sealant agent having a predetermined adhesiveness, a predetermined viscosity, and a predetermined fluidity as a conventional sealant layer does. The sealant layer <NUM> is formed by, for example, applying the sealant agent on the tire inner cavity i side of the tread portion <NUM>.

When a nail penetrates the tread portion <NUM>, the sealant agent is adhered on surroundings of the nail projecting to the inside of the tire inner cavity i, so as to cover the nail. Consequently, the sealant agent prevents leakage of the air inside the tire inner cavity i. Meanwhile, when the nail comes off from the tread portion <NUM> so as to form a through-hole in the tread portion <NUM>, the sealant agent enters the through-hole according to the internal pressure of the tire or movement of the nail. The self-sealing sealant layer <NUM> in the present embodiment essentially has these two functions.

The sealant layer <NUM> is preferably formed in, for example, a region in which nail treading or the like is likely to occur. From such a viewpoint, the sealant layer <NUM> is preferably formed in a range corresponding to a ground contact region of the tread portion <NUM>. In another mode, the sealant layer <NUM> may be disposed so as to extend beyond the range corresponding to the ground contact region of the tread portion <NUM>.

In the present description, the "ground contact region of the tread portion" is a region in which ground contact occurs in a standard running state of the pneumatic tire <NUM> and is defined as, for example, a region in which contact occurs when: a normal load is applied to the pneumatic tire <NUM> in the normal state; and the pneumatic tire <NUM> is pressed against a flat surface at a camber angle of <NUM>°. Here, the normal load refers to a load that is defined, in a standard system including a standard on which the pneumatic tire <NUM> is based, by the standard for each tire. The normal load is the "maximum load capacity" in the JATMA standard, the maximum value indicated in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, or the "LOAD CAPACITY" in the ETRTO standard.

The sealant agent typically contains a rubber component, a liquid polymer, a crosslinking agent, and the like.

As the rubber component of the sealant agent, a butyl-based rubber such as isobutylene-isoprene rubber or a halogenated isobutylene-isoprene rubber is used, for example. As the rubber component, a rubber component in which the butyl-based rubber and a diene-based rubber have been blended may be used. In this case, the amount of the butyl-based rubber contained in <NUM> parts by weight of the rubber component is preferably not smaller than <NUM> parts by weight in order to ensure the fluidity of the sealant agent.

Examples of the liquid polymer of the sealant agent include liquid polybutene, liquid polyisobutene, liquid polyisoprene, liquid polybutadiene, liquid poly-α-olefin, liquid isobutylene, liquid ethylene-α-olefin copolymers, liquid ethylene-propylene copolymers, liquid ethylene-butylene copolymers, and the like. Among these liquid polymers, liquid polybutene is particularly preferable from the viewpoint of the adhesiveness of the sealant agent.

Although the amount of the liquid polymer of the sealant agent only has to be determined as appropriate in consideration of the adhesiveness of the sealant agent, the amount of the liquid polymer contained per <NUM> parts by weight of the rubber component is preferably not smaller than <NUM> parts by weight and more preferably not smaller than <NUM> parts by weight. Meanwhile, the amount of the liquid polymer contained per <NUM> parts by weight of the rubber component is preferably not larger than <NUM> parts by weight and more preferably not larger than <NUM> parts by weight in consideration of the fluidity and the like of the sealant agent.

As the crosslinking agent of the sealant agent, a conventionally-used compound can be used, and, for example, an organic peroxide is preferable. Use of the butyl-based rubber and the liquid polymer in an organic peroxide crosslinking system leads to improvement in adhesiveness, sealing performance, fluidity, processability, and the like. As the organic peroxide, for example, acyl peroxides are preferable, and dibenzoyl peroxide is particularly preferable.

The amount of the organic peroxide (crosslinking agent) contained per <NUM> parts by weight of the rubber component is preferably not smaller than <NUM> parts by weight and more preferably not smaller than <NUM> part by weight. If the amount is smaller than <NUM> parts by weight, the crosslink density might decrease, resulting in flow of the sealant agent. Regarding the upper limit of this amount, the amount is preferably not larger than <NUM> parts by weight and more preferably not larger than <NUM> parts by weight. If the amount is larger than <NUM> parts by weight, the crosslink density might increase, resulting in decrease in sealing performance.

<FIG> is a partial front view of the tire inner cavity i. As shown in <FIG> and <FIG>, the sealant layer <NUM> includes, in the front view of the tire inner cavity i, a first region <NUM> having a surface that is covered with the sound absorbing material <NUM> and a second region <NUM> having a surface that is not covered with the sound absorbing material <NUM>. In the present embodiment, the second region <NUM> is formed on each of both sides in the tire axial direction of the first region <NUM>.

The sealant layer <NUM> in the present embodiment is formed such that, in a first tire cross section (<FIG>), a sealant layer thickness of at least a part of the first region <NUM> is smaller than a sealant layer thickness of each of the second regions <NUM>. Here, the first tire cross section means an arbitrarily-selected cross section taken in the tire circumferential direction. The cross section can be captured through, for example, CT scanning.

Since the first region <NUM> has a relatively small sealant layer thickness, the weight of the sealant layer <NUM> is decreased, and thus increase in the weight of the tire is suppressed. Here, in general, the air sealing performance tends to be decreased at a portion having a small sealant layer thickness. However, the surface of the portion having a small sealant layer thickness is covered with the sound absorbing material <NUM> so that the air sealing performance at the portion is maintained. For example, some of fragments of the sound absorbing material <NUM> fractured upon contact with a nail enter the resultant through-hole, thereby being able to supplement the air sealing performance.

Although the above requirement of the sealant layer thickness only has to be satisfied in an arbitrarily-selected first tire cross section taken in the tire circumferential direction, the requirement is preferably satisfied at a plurality of locations in the tire circumferential direction. Consequently, the above advantageous effects are obtained at the plurality of locations in the tire circumferential direction. In a more preferable mode, the above requirement of the sealant layer thickness is satisfied over a range that is preferably not lower than <NUM>%, more preferably not lower than <NUM>%, and further preferably <NUM>% of the entire range, in the tire circumferential direction, in which the sound absorbing material <NUM> is disposed. Consequently, the above advantageous effects can be further assuredly exhibited.

From another viewpoint, in the first tire cross section, an average sealant layer thickness of the first region <NUM> may be set to be smaller than an average sealant layer thickness of the second region <NUM>. In such a mode as well, the above advantageous effects can be exhibited. In the present description, each average sealant layer thickness is calculated as a value obtained by dividing the cross-sectional area of the corresponding region of the sealant layer <NUM> in the first tire cross section by the length in the tire axial direction of the region.

In order to assuredly exhibit the above advantageous effects, the first region <NUM> of the sealant layer <NUM> includes a small-thickness portion 10a having a sealant layer thickness t1 of <NUM> to <NUM>.

In a particularly preferable mode, the small-thickness portion 10a is preferably formed so as to occupy, in the tire axial direction, not lower than <NUM>% of the first region <NUM>. In a further preferable mode, the small-thickness portion 10a is preferably formed so as to occupy the entire range in the tire axial direction of the first region <NUM>. In these modes, the above advantageous effects are further assuredly exhibited. In a more preferable mode, the sealant layer thickness t1 of the small-thickness portion 10a is set to be not larger than <NUM> or set to be not larger than <NUM>.

The second region <NUM> of the sealant layer <NUM> has a surface that is not covered with the sound absorbing material <NUM>. Thus, the advantageous effect of supplementing the air sealing performance by the sound absorbing material <NUM> is not obtained in the second region <NUM>. Therefore, the second region <NUM> includes a large-thickness portion 10b having a sealant layer thickness t2 larger than the sealant layer thickness t1 of the small-thickness portion 10a. From the viewpoint of suppressing increase in the weight of the tire, increase in manufacturing cost therefor, and the like, the sealant layer thickness t2 of the large-thickness portion 10b is set as appropriate so as to fall within a range of, for example, <NUM> to <NUM> and more preferably <NUM> to <NUM>.

As shown in <FIG>, the second regions <NUM> of the sealant layer <NUM> in the present embodiment include gradual decrease portions 102a each having a sealant layer thickness that is decreased toward the first region <NUM>. In a preferable mode, each of the gradual decrease portions 102a is connected to a corresponding end portion of the first region <NUM> (i.e., the end portion on the sound absorbing material <NUM> side). Such a gradual decrease portion 102a contributes to smoothing a weight distribution in the tire axial direction of the sealant layer <NUM> and thus contributes to suppressing undesirable vibrations and the like during running with the tire.

Each of the second regions <NUM> in the present embodiment includes the corresponding gradual decrease portion 102a and a fixed-thickness portion 102b having a sealant layer thickness that is substantially fixed. The gradual decrease portion 102a in the present embodiment has a thickness that is continuously decreased from the sealant layer thickness (the thickness of the corresponding large-thickness portion) t2 of the fixed-thickness portion 102b of the second region <NUM> to the sealant layer thickness t1 of the small-thickness portion 10a of the first region <NUM>. In each of the left and right second regions <NUM>, the length in the tire axial direction of the corresponding gradual decrease portion 102a may be, for example, about <NUM> to <NUM>% of the width in the tire axial direction of the second region <NUM>. From the viewpoint of the above advantageous effect of suppressing vibrations, the taper angle of the gradual decrease portion 102a is preferably <NUM> to <NUM>°.

In the present embodiment, as shown in <FIG>, in the front view of the tire inner cavity i, an area A of each of the large-thickness portions 10b in the sealant layer <NUM> (i.e., the length in the tire axial direction of the large-thickness portion 10b×the length in the tire circumferential direction of the large-thickness portion 10b) is set to be not lower than <NUM>% and more preferably not lower than <NUM>% of a total area B of the corresponding second region <NUM>. Consequently, the air sealing performance in each second region <NUM> of the sealant layer <NUM> is improved.

The area A of the large-thickness portion 10b may exceed <NUM>% of the total area B of the second region <NUM>. <FIG> shows an example of such a sealant layer <NUM>. As shown in <FIG>, the first region <NUM> of the sealant layer <NUM> includes the small-thickness portion 10a and large-thickness portions 10b. In such an embodiment, the proportion of the small-thickness portion 10a is decreased, and thus a more excellent air sealing performance can be provided. Meanwhile, if the area A of the large-thickness portion 10b is excessively large relative to the total area B of the second region <NUM>, the weight of the sealant layer <NUM> is increased, whereby the weight of the tire might be excessively increased. Therefore, the area A of the large-thickness portion 10b is preferably not higher than <NUM>% of the total area B of the second region <NUM> in order to sufficiently ensure the air sealing performance in the first region <NUM> while decreasing the weight of the sealant layer <NUM>.

If the large-thickness portions 10b are included in the first region <NUM>, it is particularly preferable that, as shown in <FIG>: each of the large-thickness portions 10b is formed at the corresponding end portion in the tire axial direction of the first region <NUM>; and the small-thickness portion 10a is formed at the center portion of the first region <NUM>. Consequently, in the present embodiment, balance in the weight of the sealant layer <NUM> in the first region <NUM> thereof is substantially attained between both sides of a tire equator. Such an embodiment leads to inhibition of, for example, occurrence of undesirable vibrations caused by the sealant layer <NUM> during running with the tire.

Although each embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described specific disclosure and can be implemented with various changes being made within the scope of the claims.

Next, more specific and non-limiting examples of the present invention will be described.

A plurality of types of pneumatic tires each having the basic structure of the tire in <FIG> and each including a sealant layer and a sound absorbing material were produced as samples on the basis of specifications indicated in Tables <NUM> and <NUM>. Specific configurations of the sealant layers are also shown in <FIG>. Specifications common to the tires are as follows.

The formula of each sealant agent was as follows (unit: parts by weight), and the specific gravity thereof was <NUM>.

Next, each of the tires was evaluated regarding the weight and the air sealing performance of the sealant layer. For the air sealing performance, each of the test tires was mounted to a rim first, and the internal pressure thereof was adjusted to the initial internal pressure. Then, <NUM> nails were driven into the tread portion. Among the nails, <NUM> nails were driven so as to penetrate the first region of the sealant layer, <NUM> nails were driven so as to penetrate the left-side second region, and <NUM> nails were driven so as to penetrate the right-side second region. The size of each of the nails was such that the length thereof was <NUM> and the outer diameter thereof was <NUM>. Then, at the elapse of <NUM> minutes after the nails were driven, all the nails were pulled out of the tread portion. Then, high-pressure air was supplied into the tire again, and the tire was left for <NUM> hours. Thereafter, in each of the first region and the second regions, the number of the locations of nail holes that had been sealed by the sealant layer was measured. In Tables <NUM> and <NUM>, a larger numerical value indicates a better air sealing performance.

Claim 1:
A pneumatic tire (<NUM>) comprising:
a tread portion (<NUM>);
a self-sealing sealant layer (<NUM>) disposed on a tire inner cavity (i) side of the tread portion (<NUM>); and
a sound absorbing material (<NUM>), in a form of a sponge, fixed to the sealant layer (<NUM>), wherein
the sealant layer (<NUM>) includes, in a front view of the tire inner cavity (i), a first region (<NUM>) having a surface that is covered with the sound absorbing material (<NUM>) and a second region (<NUM>) having a surface that is not covered with the sound absorbing material (<NUM>), and,
in a first tire cross section, a sealant layer thickness of at least a part of the first region (<NUM>) is smaller than a sealant layer thickness of the second region (<NUM>),
wherein the first region (<NUM>) includes a small-thickness portion (10a) having a sealant layer thickness t1 of <NUM> to <NUM>, the second region (<NUM>) includes a large-thickness portion (10b) having a sealant layer thickness t2 larger than the sealant layer thickness t1 of the small-thickness portion (10a)
characterised in that in the front view of the tire inner cavity (i), an area A of the large-thickness portion (10b) in the sealant layer (<NUM>) is not lower than <NUM>% of a total area B of the second region (<NUM>).