Patent Description:
<CIT> proposes a pneumatic tire that has both puncture sealing performance and road noise reducing performance. The pneumatic tire proposed therein has a puncture-preventive sealant layer that is made of a sealant material and is provided inward of the inner liner in the tire radial direction, and a sound absorbing layer that is made of a sponge material or the like and is provided inward of the sealant layer in the tire radial direction.

<CIT> discloses a tire wherein a sealant layer is present radially inside of the tread, a closed-cell foam ring with an airtight effect is placed on the inner surface of the sealant layer, and a sound-absorbing open-cell foam ring is arranged on the inner surface of the closed-cell foam ring.

<CIT>, <CIT> and <CIT> disclose tires having sound dampers made of porous material placed on the inner surface of the tire.

However, in the above-described pneumatic tire, for example, when a puncture hole is increased due to the tire treading on a thick nail or the like, there are difficulties in sufficiently sealing the puncture hole using the sealant material, and therefore, the puncture sealing performance is not sufficiently exhibited.

The object of the present invention is to provide a pneumatic tire capable of sufficiently exhibiting puncture sealing performance even when a puncture hole is large.

A pneumatic tire according to the present invention includes: a puncture-preventive sealant layer provided on an inner peripheral surface of a tread portion; and a sound damper provided on an inner peripheral surface of the sealant layer. The sound damper includes a sponge material having closed cell foam, has an air permeability of not higher than <NUM>/cm<NUM>/s, and has a hardness of not higher than <NUM> N/<NUM><NUM>.

In the pneumatic tire of the present invention, the sound damper preferably has a tensile strength of not less than <NUM> kPa.

In the pneumatic tire of the present invention, the sound damper preferably has a thickness of not less than <NUM>.

The "air permeability" of the sponge material is measured in accordance with the following measuring manner, in the present invention. As shown in <FIG>, a sample A of a sponge material having a width W of <NUM>, a depth L of <NUM>, and a thickness T of <NUM> is adhered to a flat plate B having a thickness of <NUM> and having a hole H with a diameter of <NUM> (corresponding to an opening area of <NUM><NUM>). At this time, the sample A is adhered to the flat plate B such that the center of a surface, of the sample A, having the width W × the depth L is located at the hole H. A pressure P2 on the sample A (sponge material) side is increased to set, as <NUM> kPa, the pressure difference (P2 - P1) between the pressure P2 and a pressure P1 on the flat plate B side. At this time, a flow rate (mL) per second (s) of air leaking from the hole H is measured. This flow rate is converted to a flow rate per opening area of <NUM><NUM> and the obtained flow rate represents the air permeability (mL/cm<NUM>/s).

The hardness of the sponge material is measured in accordance with Method D for a hardness test specified in Section <NUM> of JIS-K6400-<NUM>, entitled "Flexible cellular polymeric materials - Physical properties - Part <NUM>: Determination of hardness (indentation technique) and stress-strain characteristics in compression", in the present invention. Specifically, a sponge material is placed so as to be flat, and a round pressing plate having a diameter of <NUM> is placed on the sponge material, and pushed over a distance corresponding to <NUM>% of the thickness (original thickness) of the sponge material under no load. Thereafter, the sponge material is restored. The plate is pushed again over a distance corresponding to <NUM>% of the original thickness, and left in a stationary state for <NUM> seconds. The value of a load measured at this time is expressed in newtons (N).

The tensile strength of the sponge material is measured in accordance with Section <NUM>, "Tensile Strength and Elongation", of JIS-K6400-<NUM>, entitled "Flexible cellular polymeric materials - Physical properties - Part <NUM>: Determination of tensile strength, elongation at break and tear strength", in the present invention. A value measured for a No. <NUM> dumbbell-shaped test piece represents the tensile strength of the sponge material.

In the present invention, as described above, the sound damper includes a sponge material having closed cell foam, and has an air permeability of not higher than <NUM>/cm<NUM>/s. The air permeability is measured based on the above-described measuring manner.

In the present invention, even if a puncture hole is large and puncture sealing is not sufficiently achieved by the sealant material, since the sound damper has an air permeability of not higher than <NUM>/cm<NUM>/s and thus has excellent hermetic properties, the sound damper itself reduces air flowing through the puncture hole.

Furthermore, the sound damper having high hermetic properties acts to press the sealant material around a puncture hole. Therefore, the sealant material can be easily pushed into the puncture hole, thereby also enhancing the effect of the sealant material for sealing the puncture hole. The interaction between these effects improves the puncture sealing performance and increases the puncture sealing success rate.

Embodiments of the present invention will be described below in detail.

As shown in <FIG>, a pneumatic tire <NUM> according to the present embodiment is a tubeless tire, and includes a puncture-preventive sealant layer <NUM> which is provided on an inner peripheral surface <NUM> of a tread portion <NUM>, and a sound damper <NUM> which is provided on an inner peripheral surface <NUM> of the sealant layer <NUM>.

In this example, the pneumatic tire <NUM> includes a carcass <NUM> that extends from the tread portion <NUM> to bead cores <NUM> of bead portions <NUM> through sidewall portions <NUM>, and a belt layer <NUM> that is located inward of the tread portion <NUM> and outward of the carcass <NUM> in the radial direction.

The carcass <NUM> includes one or more carcass plies 6A having carcass cords aligned with each other. In the present embodiment, the carcass <NUM> includes one carcass ply 6A. The carcass ply 6A has a body portion 6a extending on and between the bead cores <NUM>, <NUM>, and turn-up portions 6b turned up around the bead cores <NUM> at both ends of the body portion 6a. A bead apex rubber <NUM> which reinforces the bead and extends outward from the bead core <NUM> in the tire radial direction is provided between the body portion 6a and each turn-up portion 6b.

The belt layer <NUM> includes a plurality of belt plies having belt cords aligned with each other. For example, the belt layer <NUM> includes two belt plies 7A, 7B. In order to enhance the high speed durability of the tire, a band layer (not shown) including a helically wound band cord can be provided outward of the belt layer <NUM> in the radial direction.

An inner liner rubber layer <NUM> is provided inward of the carcass <NUM>. The inner liner rubber layer <NUM> is made of air-impermeable rubber such as isobutylene-isoprene-rubber, and hermetically maintains the tire internal pressure.

The sealant layer <NUM> is provided on the inner peripheral surface <NUM> of the tread portion <NUM>. As a sealant material <NUM> of the sealant layer <NUM>, those described in <CIT> are suitably used. Specifically, the sealant material <NUM> of the present embodiment contains a rubber component, a liquid polymer, a crosslinking agent, and the like.

As the rubber component, butyl-based rubber such as isobutylene-isoprene-rubber and halogenated isobutylene-isoprene-rubber is used. As the rubber component, the butyl-based rubber is preferably used in conjunction with diene-based rubber.

Examples of the liquid polymer include liquid polybutenes, liquid polyisobutenes, liquid polyisoprenes, liquid polybutadienes, liquid poly-α-olefins, liquid isobutylene, liquid ethylene/α-olefin copolymers, liquid ethylene-propylene copolymers, and liquid ethylenebutylene copolymers. Among them, liquid polybutenes are preferable in terms of adhesiveness or the like.

As the crosslinking agent, known compounds can be used, and organic peroxides are preferable. The use of the butyl-based rubber and the liquid polymer in the organic peroxide crosslinking agent improves adhesiveness, sealing performance, fluidity, and workability.

To the sealant material <NUM>, a crosslinking activator (vulcanization accelerator), an inorganic filler, a plasticizer, or the like can be added as appropriate.

The sealant material <NUM> which has been produced by preparing and mixing the above-described materials is applied to the inner peripheral surface <NUM> of the tread portion <NUM> of a previously vulcanization-molded tire, to form the sealant layer <NUM>. Preferably, as described in <CIT>, for example, the sealant material <NUM> is continuously extruded from a twin-screw kneading extruder and helically adhered to the inner peripheral surface <NUM> of the tread portion <NUM> of a rotating tire. The tire to which the sealant material <NUM> has been applied is heated to vulcanize the sealant material <NUM>. Thus, the sealant layer <NUM> having excellent sealing performance is formed.

A width 11W of the sealant layer <NUM> in the tire axial direction is not particularly limited. However, the width 11W is preferably <NUM> to <NUM>% of a tread ground-contact width TW. The lower limit of the width 11W is preferably not less than <NUM>% of the tread ground-contact width TW and more preferably not less than <NUM>% thereof. The upper limit of the width 11W is preferably not greater than <NUM>% of the tread ground-contact width TW and more preferably not greater than <NUM>% thereof.

The tread ground-contact width TW refers to the maximum width, in the tire axial direction, of a ground contact surface which is in contact with the ground when a normal load is applied to a tire mounted on a normal rim and inflated to a normal internal pressure. The "normal rim" represents a rim that is defined, in a standard system including a standard with which the tire complies, by the standard for each tire, and is, for example, the "standard rim" in the JATMA standard, the "Design Rim" in the TRA standard, or the "Measuring Rim" in the ETRTO standard. The "normal internal pressure" represents an air pressure defined by the standard for each tire, and is the "maximum air pressure" in the JATMA standard, the maximum value recited in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, or the "INFLATION PRESSURE" in the ETRTO standard. In the case of a tire for a passenger car, the normal internal pressure is <NUM> kPa. The "normal load" represents a load defined by the standard for each tire, and is the "maximum load capacity" in the JATMA standard, the maximum value recited in the table "TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES" in the TRA standard, or the "LOAD CAPACITY" in the ETRTO standard.

In the description herein, unless otherwise specified, dimensions and the like of the components of the tire are represented by values specified in a state where the tire is inflated to the normal internal pressure and no load is applied to the tire.

A thickness 11t of the sealant layer <NUM> is preferably not less than <NUM>, more preferably not less than <NUM>, and even more preferably not less than <NUM>. The upper limit of the thickness 11t is preferably not greater than <NUM>, more preferably not greater than <NUM>, and even more preferably not greater than <NUM>. If the thickness 11t is less than <NUM>, there are difficulties in assuredly sealing a puncture hole. Conversely, if the thickness 11t is greater than <NUM>, the effect of sealing the puncture hole is substantially no longer improved, and the mass of the tire disadvantageously increases.

The sound damper <NUM> is made of a sponge material and is provided on the inner peripheral surface <NUM> of the sealant layer <NUM>. The sound damper <NUM> is adhered to the sealant layer <NUM> by the adhesiveness of the sealant material <NUM>.

The sound damper <NUM> extends in the tire circumferential direction. In particular, the sound damper <NUM> preferably forms an annular shape in which both ends of the sound damper <NUM> in the tire circumferential direction meet each other. Both the ends of the sound damper <NUM> in the tire circumferential direction may be spaced apart from each other. In that case, the spaced distance is preferably not greater than <NUM>, more preferably not greater than <NUM>, and even more preferably not greater than <NUM>.

As the sponge material of the sound damper <NUM>, closed cell foam obtained by foaming of rubber or a synthetic resin is used. Examples of the rubber foam include chloroprene rubber sponge, ethylene propylene rubber sponge, and nitrile rubber sponge. Examples of the synthetic resin foam include polyurethane-based sponges (e.g., ether-based polyurethane sponges, ester-based polyurethane sponges, and ether/ester-based polyurethane sponges), and polyethylene-based sponges (e.g., polyethylene sponge).

In order to allow the sponge material to exhibit the sound damping performance, the density of the sponge material is preferably not greater than <NUM>/m<NUM>, more preferably not greater than <NUM>/m<NUM>, and even more preferably not greater than <NUM>/m<NUM>. The lower limit of the density is preferably not less than <NUM>/m<NUM>, more preferably not less than <NUM>/m<NUM>, and even more preferably not less than <NUM>/m<NUM>.

The sound damper <NUM> has an air permeability of not higher than <NUM>/cm<NUM>/s.

The "air permeability" is measured in accordance with the above-described measurement manner. For example, the air permeability of not higher than <NUM>/cm<NUM>/s is assumed to correspond to a value of an air leakage (an amount of air leaking through a hole having a diameter of <NUM>) that causes a pressure decrease of <NUM> to <NUM> kPa per day in a tire, for a passenger car, inflated with air to <NUM> kPa.

The sound damper <NUM> having such a configuration has a low air permeability, and has excellent hermetic properties. Therefore, as shown in <FIG>, for example, even if a puncture hole H is large and the sealant material <NUM> fails to sufficiently perform puncture sealing, the sound damper <NUM> itself can seal the puncture hole H to reduce the flowing-out of air. This effect may be referred to as "sound damper's sealing effect".

Furthermore, the sound damper <NUM> has excellent hermetic properties and thus acts to press the sealant material <NUM> around the puncture hole H. Therefore, the sealant material <NUM> can be easily pushed into the puncture hole H, which enhances an effect of the sealant material <NUM> for sealing the puncture hole H. This effect may be referred to as "sealant material pushing effect". The interaction between the sound damper's sealing effect and the sealant material pushing effect can improve the puncture sealing performance, and enhance puncture sealing success rate.

A thickness 12t of the sound damper <NUM> is preferably not less than <NUM>. Therefore, a foreign object <NUM> such as a nail is unlikely to penetrate through the sound damper <NUM>, and the above-described effects can be more assuredly exhibited. A result of market research indicates that most foreign objects sticking into a tire in the market each have a length of not greater than <NUM>. Therefore, in consideration of the tire thickness, if the thickness 12t of the sound damper <NUM> is not less than <NUM>, the foreign object <NUM> can be almost assuredly prevented from penetrating through the sound damper <NUM>.

If the air permeability is higher than <NUM>/cm<NUM>/s, the sound damper <NUM> allows air to easily pass, and thus, the sound damper's sealing effect is not sufficiently exhibited. In addition, a sufficient sealant material pushing effect cannot be expected. From this standpoint, the upper limit of the air permeability is preferably not higher than <NUM>/cm<NUM>/s, more preferably not higher than <NUM>/cm<NUM>/s, and even more preferably not higher than <NUM>/cm<NUM>/s. The air permeability does not particularly have a lower limit, i.e., the lower the better.

If the thickness 12t of the sound damper <NUM> is less than <NUM>, the foreign object <NUM> such as a nail may penetrate through the sound damper <NUM>, and, for example, air leaks through the generated through hole, whereby the sound damper's sealing effect is not sufficiently exhibited. Therefore, the lower limit of the thickness 12t is preferably not less than <NUM> and more preferably not less than <NUM>. However, if the thickness 12t is excessively great, the mass increases, leading to separation of the sound damper <NUM> from the sealant layer <NUM> due to centrifugal force. In addition, when a rim is removed, the workability may be adversely affected. Therefore, the upper limit of the thickness 12t is preferably not greater than <NUM>, more preferably not greater than <NUM>, and even more preferably not greater than <NUM>.

During running, a force is applied to the sound damper <NUM> in a direction in which the thickness 12t is reduced due to centrifugal force. However, the sound damper <NUM> formed of a sponge material having a low air permeability is supported by gas in the closed cell foam, and therefore, the reduction of volume is small, resulting in sound damping performance being stably exhibited.

A width 12W of the sound damper <NUM> in the tire axial direction may be less than, equal to, or greater than the width 11W of the sealant layer <NUM>. In a case where the width 12W is less than the width 11W (12W < 11W), the puncture sealing performance can be exhibited by performance intrinsic to the sealant layer <NUM> also at a portion where only the sealant layer <NUM> is present. Also in a case where the width 12W is equal to or greater than the width 11W (12W ≥ 11W), the sound damper's sealing effect and the sealant material pushing effect can be exhibited throughout the entire surface of the sealant layer <NUM>. However, the width 12W is preferably not less than <NUM>% of the width 11W, more preferably not less than <NUM>% thereof, and even more preferably not less than <NUM>% thereof, in terms of balance among sound damping performance, weight, rim mounting workability, and the like. The upper limit of the width 12W is preferably not greater than <NUM>% of the width 11W, more preferably not greater than <NUM>% thereof, and even more preferably not greater than <NUM>% thereof. In a case where the sound damper <NUM> is applied to a tire having a small width, if the width 12W of the sound damper <NUM> is excessively small although the width 12W is in the above-described range, the sound damper <NUM> is likely to fall down. Therefore, the width 12W is also preferably not less than the thickness 12t.

In order to allow the sound damper <NUM> to further enhance the sealant material pushing effect, the sound damper <NUM> has a hardness of not higher than <NUM> N/<NUM><NUM>. Thus, as exaggerated in <FIG>, the sound damper <NUM> is bent to intensively press a portion of the sealant material <NUM> around the puncture hole H, so that an effectiveness of pushing the sealant material <NUM> into the puncture hole H and the flow of the sealant material <NUM> can be enhanced. Meanwhile, if the sound damper <NUM> has a hardness of higher than <NUM> N/<NUM><NUM> and is hard, the pressing force is dispersed over a wide range, so that there are difficulties in intensively pressing a portion of the sealant material <NUM> around the puncture hole. From this standpoint, the hardness of the sound damper <NUM> is preferably not higher than <NUM> N/<NUM><NUM> and more preferably not higher than <NUM> N/<NUM><NUM>. However, if the hardness is excessively low, the flow of the sealant material <NUM> deteriorates. Therefore, the lower limit of the hardness is preferably not less than <NUM> N/<NUM><NUM>, more preferably not less than <NUM> N/<NUM><NUM>, and even more preferably not less than <NUM> N/<NUM><NUM>.

The sound damper <NUM> also preferably has a tensile strength of not less than <NUM> kPa. If the tensile strength is less than <NUM> kPa, when the foreign object <NUM> sticks into the sound damper <NUM> as shown in <FIG>, a portion of the sponge material (the sound damper <NUM>) is more likely to be torn off due to the foreign object <NUM> to which the sealant material <NUM> adheres. When the foreign object <NUM> is removed from the tire, a sponge strip <NUM> having been torn off is left in the puncture hole H as shown in <FIG>, so that puncture sealing by the sealant material <NUM> tends to be hindered. From this standpoint, the tensile strength of the sound damper <NUM> is preferably not less than <NUM> kPa and more preferably not less than <NUM> kPa. The upper limit of the tensile strength is not particularly limited, i.e., the higher the better.

From the standpoint that the sponge material is prevented from being torn off, it is preferable that the sound damper <NUM> can easily come off the sealant material. Thus, when a sticking foreign object is pulled out, the sponge material is unlikely to be pulled and torn off, and therefore, puncture sealing is not hindered.

Therefore, adhesion between the sound damper <NUM> and the sealant material as specified by the following measuring manner is preferably not greater than <NUM> N/cm<NUM>. In the measuring manner, a rectangular-parallelepiped-shaped test piece having a <NUM> × <NUM> square adhesion surface and a thickness of <NUM> is initially cut out of the sound damper <NUM>, and the adhesion surface of the test piece is adhered to the flat sealant layer <NUM>. A surface opposite to the adhesion surface of the test piece is firmly adhered to a jig. Next, the test piece is pulled perpendicularly relative to the sealant layer <NUM> by using the jig, and a force is measured when the test piece comes off the sealant layer <NUM>. This force is divided by the area of the adhesion surface of the test piece, to obtain the adhesion. The tensile speed of the jig is <NUM>/min. The adhesion is preferably not greater than <NUM> N/cm<NUM> and more preferably not greater than <NUM> N/cm<NUM>. The lower limit of the adhesion is preferably not less than <NUM> N/cm<NUM>, more preferably not less than <NUM> N/cm<NUM>, and even more preferably not less than <NUM> N/cm<NUM>.

Although the preferred embodiments of the present invention have been described above in detail, the present invention is not limited to the illustrated embodiments, and various modifications can be made to implement the present invention.

Pneumatic tires (tire size: <NUM>/55R17) which had the basic structure shown in <FIG> and to which sound dampers having specifications indicated in Table <NUM> were adhered were produced as test tires. The puncture sealing success rate (puncture sealing performance) of each test tire was evaluated. Example <NUM> is not according to the invention.

Ether/ester-based polyurethane sponges (density: <NUM>/m<NUM>) were used as the respective sound dampers. The test tires had substantially the same specifications, except for the sound dampers.

Fifty nails (nails in JIS N150 each having a diameter of <NUM> and a length of <NUM>) were driven into a groove bottom portion in the tire equator of the tread portion of each test tire inflated to an internal pressure (<NUM> kPa) such that the nails were dispersed in the circumferential direction. After the tire was left as it was in an environment having room temperature of <NUM> for one hour, the nails were pulled out, soapy water was applied to the puncture holes, and the presence or absence of air leakage was checked. The puncture sealing success rate was obtained and evaluated from the number of puncture holes that did not cause air leakage. The higher the value is, the more excellent puncture sealing performance is.

As indicated in Table <NUM>, it can be confirmed that the products of the examples allowed enhancement of the puncture sealing success rate.

The sealant layer had a thickness of <NUM>, and had a sealant material having a composition indicated in Table <NUM>. The chemicals indicated in Table <NUM> are as follows.

Claim 1:
A pneumatic tire (<NUM>) comprising:
a puncture-preventive sealant layer (<NUM>) provided on an inner peripheral surface (<NUM>) of a tread portion (<NUM>); and
a sound damper (<NUM>) provided on an inner peripheral surface (<NUM>) of the sealant layer (<NUM>),
the sound damper (<NUM>) including a sponge material having closed cell foam,
characterised in that
the sound damper (<NUM>) has an air permeability of not higher than <NUM>/cm<NUM>/s, and the sound damper (<NUM>) has a hardness of not higher than <NUM> N/<NUM><NUM>,
wherein the air permeability is measured by adhering a sample (A) of the sponge material having a width (W) of <NUM>, a depth (L) of <NUM>, and a thickness (T) of <NUM> to a flat plate (B) having a thickness of <NUM> and having a hole (H) with a diameter of <NUM>, corresponding to an opening area of <NUM><NUM>, then adhering the sample (A) to the flat plate (B) such that the center of a surface, of the sample (A), having the width (W) × the depth (L) is located at the hole (H), increasing a pressure (P2) on the sponge material sample (A) side to set, as <NUM> kPa, the pressure difference P2 - P1 between the pressure (P2) and a pressure (P1) on the flat plate (B) side, then measuring a flow rate, in mL per second, of air leaking from the hole (H), and then converting the flow rate to a flow rate per opening area of <NUM><NUM>, and the obtained flow rate represents the air permeability, in mL/cm<NUM>/s, and
wherein the hardness of the sponge material is measured in accordance with Method D for a hardness test specified in Section <NUM> of JIS-K6400-<NUM>.