Tire

Abstract

To provide a tire having improved drainage performance.SOLUTION: A tire includes a plurality of grooves (16, 18, 20, 22, 24, and 26) which are provided on a tread surface (14), where a porous layer (30a and 30b) in which fine particles of hydrophobic oxides are laminated in a three dimensional network shape is formed, on at least one of a groove bottom (17a and 23a) and a groove wall (17b and 23b) of at least one (16a and 22b) of the grooves, and where mean size of primary particles of the fine particles of hydrophobic oxides is 3 nm or more and 100 nm or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a tire having a porous layer formed on the groove surface. [Background technology]

[0002] Conventionally, a tire has been known that has a highly self-cleaning surface layer on at least a portion of the groove bottom or groove wall (Patent Document 1). In the tire disclosed in Patent Document 1, the surface layer is made of fine particles of fluororesin, which makes it possible to improve the drainage capacity of the tire's contact surface regardless of the land pattern or groove shape, and it is said that this enables stable high-speed driving in rainy weather. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-99712 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, there has been a demand for the development of tires with improved drainage performance in order to suppress hydroplaning to a high level.

[0005] The present invention has been made in view of the above circumstances, and has an object to provide a tire with improved drainage performance. [Means for solving the problem]

[0006] The tire according to the present invention is characterized in that it has a plurality of grooves on the tread surface, and at least one of the grooves has a porous layer formed on at least one of the groove bottom and groove wall, the porous layer being made of hydrophobic oxide microparticles stacked in a three-dimensional network pattern, and the hydrophobic oxide microparticles have an average primary particle diameter of 3 nm or more and 100 nm or less. [Effects of the Invention]

[0007] In the tire according to the present invention, a porous layer is formed on at least one of the groove bottom and groove wall, in which hydrophobic oxide fine particles having a specific average primary particle diameter are layered in a three-dimensional network pattern, thereby enabling the groove bottom and / or groove wall to exhibit the so-called lotus effect, and ultimately enabling the exhibiting of high-level drainage performance. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a plan view showing an example of a tread pattern of a tire according to this embodiment. [Figure 2] FIG. 2 is a tire meridian cross-sectional view of a circumferential main groove formed in the tire shown in FIG. [Figure 3] FIG. 3 is a tire meridian cross-sectional view of lug grooves formed in the tire shown in FIG. [Figure 4] 4 is a meridian cross-sectional view of a tire showing a region where a porous layer is formed in the circumferential main groove shown in FIG. [Figure 5] FIG. 5 is a plan view showing a suitable region for forming a porous layer in another example of the tread pattern of the tire according to the present embodiment. [Figure 6] FIG. 6 is a plan view showing a suitable region for forming a porous layer in a tire having a tread pattern different from that of the tire shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Aspects of the present invention> The embodiments of the present invention relate to the following aspects.

[0010] [Aspect 1] A tire having a plurality of grooves on the tread surface, A tire characterized in that a porous layer formed by laminating hydrophobic oxide microparticles in a three-dimensional network pattern is formed on at least one of the groove bottom and groove wall of at least one of the grooves, and the average primary particle diameter of the oxide microparticles is 3 nm or more and 100 nm or less. [Aspect 2] The adhesion amount of the porous layer to the groove bottom and / or the groove wall is 0.05 g / mm 2 More than 50g / m 2 and the thickness of the porous layer is 0.5 μm or more and 30 μm or less. [Aspect 3] The specific surface area of ​​the porous layer measured by the BET method is 50m 2 / g or more 300m 2 / g or less. [Aspect 4] Aspect 4. The tire of any one of aspects 1 to 3, wherein the hydrophobic oxide particulate is hydrophobic silica. [Aspect 5] 5. The tire of embodiment 4, wherein the hydrophobic silica has trimethylsilyl groups on its surface. [Aspect 6] Aspect 6. The tire according to any one of aspects 1 to 5, wherein a primer layer is formed between the groove bottom and / or the groove wall and the porous layer. [Aspect 7] the porous layer is formed at least in the circumferential main groove, 7. The tire according to any one of aspects 1 to 6, wherein the porous layer is formed at least in a range from a 50% depth position to a 100% depth position, where the tread surface position is a 0% depth position and the groove bottom position is a 100% depth position. [Aspect 8] A tire according to any one of aspects 1 to 7, wherein at least a portion of the porous layer is formed in a main groove formed in a region of the central 50% of the developed width of the tire.

[0011] <Definition> In the following description, the tire radial direction refers to the direction perpendicular to the tire's rotational axis, the tire radially inner side refers to the side toward the rotational axis in the tire radial direction, and the tire radially outer side refers to the side away from the rotational axis in the tire radial direction. The tire circumferential direction refers to the direction around the rotational axis as the central axis. The tire width direction refers to the direction parallel to the rotational axis, the tire widthwise inner side refers to the side toward the tire equatorial plane (tire equator line) in the tire width direction, and the tire widthwise outer side refers to the side away from the tire equatorial plane in the tire width direction. The tire equatorial plane is a plane that is perpendicular to the tire's rotational axis and passes through the center of the tire width.

[0012] Similarly, in the following description, a regular rim refers to an "applicable rim" as defined by JATMA, a "design rim" as defined by TRA, or a "measuring rim" as defined by ETRTO.

[0013] Similarly, in the following explanation, "normal internal pressure" refers to the "maximum air pressure" specified by JATMA, the maximum value specified in "Tire Load Limits at Various Cold Inflation Pressures" specified by TRA, or the "Inflation Pressures" specified by ETRTO. Also, "normal load" refers to the "maximum load capacity" specified by JATMA, the maximum value specified in "Tire Load Limits at Various Cold Inflation Pressures" specified by TRA, or the "Load Capacity" specified by ETRTO.

[0014] <Tires> Hereinafter, an embodiment of a tire of the present invention (hereinafter referred to as "the present embodiment") will be described with reference to the drawings. Fig. 1 is a diagram showing both sides in the tire width direction with the tire equatorial plane as the reference in a plan view of a tire according to the present embodiment as seen from the outside in the tire radial direction. Note that this figure shows the tire portion in a state where it is mounted on a rim and has a normal internal pressure applied, and in an unloaded state (this is also true for other figures). In Fig. 1, the symbol Dc denotes the tire circumferential direction, and the symbol Dw denotes the tire width direction (this is also true for other figures).

[0015] The tire of this embodiment has a tread pattern shown in Fig. 1 formed continuously and regularly in the tire circumferential direction. Note that in Fig. 1, the same element is assigned a reference symbol in only one place (the same applies to other figures).

[0016] Although not shown in its entirety, the tire 10 of this embodiment has a meridian cross-sectional shape similar to that of a conventional pneumatic tire. That is, the tire 10 of this embodiment has, from the inner side to the outer side in the tire radial direction in a tire meridian cross-section (not shown), a bead portion, a sidewall portion, a shoulder portion, and a tread portion. The tire 10 also has, for example, a carcass layer extending from the tread portion to both bead portions in the tire meridian cross-section and wound around a pair of bead cores, and a belt layer and, in some cases, a belt cover layer on the tire radial direction outer side of the carcass layer.

[0017] The tread portion 12 shown in Figure 1 is made of rubber (tread rubber). The tread portion 12 has a tread surface 14 that comes into contact with the road surface when the vehicle is running. The tread surface 14 is annular and centered on the rotational axis of the tire 10, has a predetermined length in the tire width direction, and is continuous in the tire circumferential direction. A predetermined tread pattern as shown in Figure 1 is engraved on the tread surface 14.

[0018] In a tire 10 according to this embodiment, circumferential main grooves 16 (16a, 16b, 16c, 16d), circumferential sub-grooves 18 (18a, 18b), oblique grooves 20 (20a, 20b), lug grooves 22 (22a, 22b), small grooves 24 (24a, 24b), decorative grooves 26, and sipes 28 (28a, 28b, 28c, 28d) are formed on a tread surface 14 as shown in Fig. 1. The portions of the circumferential main grooves 16 and the circumferential sub-grooves 18 shown in Fig. 1 are continuous in an annular shape around the entire circumference of the tire, and the oblique grooves 20, lug grooves 22, small grooves 24, decorative grooves 26, and sipes 28 are each formed continuously and regularly in the circumferential direction of the tire. Here, the circumferential main groove refers to a groove in which the absolute value of the inclination angle of the groove width center line (a line obtained by connecting groove width center positions in the circumferential direction) relative to the tire circumferential direction is 20° or less.

[0019] In this embodiment, a groove refers to a recessed portion having a width of 1.2 mm or more, and a sipe refers to a recessed portion having a width of less than 1.2 mm.

[0020] Fig. 2 is a tire meridian cross-section of the circumferential main groove formed in the tire shown in Fig. 1, specifically a cross-section taken along line AA' in Fig. 1. In Fig. 2, the symbol Dr represents the tire radial direction (the same applies to other figures). In the example shown in Fig. 2, a porous layer 30a is formed over the entire area of ​​both the groove bottom surface 17a and the groove wall surface 17b of the groove surface 17 of the circumferential main groove 16a. In the example shown in Fig. 1, a porous layer is also formed in the circumferential main grooves 16b, 16c, and 16d, similar to the circumferential main groove 16a.

[0021] Fig. 3 is a tire meridian cross-section of lug grooves formed in the tire shown in Fig. 1, specifically a cross-section taken along line BB' in Fig. 1. In the example shown in Fig. 3, porous layers 30b are formed over the entire area of ​​both the groove bottom surface 23a and the groove wall surface 23b of the groove surface 23 of the lug groove 22b. Note that in the example shown in Fig. 1, porous layers are also formed in lug grooves not marked with reference numerals, similar to the lug groove 22b.

[0022] In the example shown in FIG. 1 having grooves 16a and 22b shown in FIGS. 2 and 3, porous layers 30a and 30b are formed over the entire groove surfaces of the circumferential main groove 16 (16a to 16d) and all lug grooves (lug groove 22b, etc.) among the multiple grooves, but this embodiment is not limited to such an example.

[0023] That is, in the tire of this embodiment, the porous layer may be formed in at least any one of the grooves (hereinafter, sometimes referred to as "specific grooves") formed on the tread surface (in the example shown in FIG. 1, the circumferential main groove 16, the circumferential sub-groove 18, the inclined groove 20, the lug groove 22, the small groove 24, and the decorative groove 26).

[0024] Furthermore, in the tire of this embodiment, the porous layer may be formed in any region of the specific groove, and does not have to be formed over the entire surface of the groove as shown in FIGS.

[0025] 2, the porous layer 30a may be formed on a portion of the groove bottom surface 17a and / or a portion of the groove wall surface 17b. Here, the portion may be any region.

[0026] 3, the porous layer 30b may be formed on a partial region of the groove bottom surface 23a and / or a partial region of the groove wall surface 23b. Here, the partial region may be any region.

[0027] The porous layers 30a and 30b shown in FIGS. 2 and 3 are formed by laminating hydrophobic oxide particles in a three-dimensional network, and the average primary particle diameter of the hydrophobic oxide particles is 3 nm or more and 100 nm or less.

[0028] Here, the term "primary particle" refers to each particle that constitutes a secondary particle formed by the condensation of particles. The primary particle diameter can be measured by scraping off the porous layer from the tire groove surface (groove bottom surface and / or groove wall surface) using, for example, a dynamic light scattering frequency analysis method or a photon correlation method.

[0029] In the tire 10 of this embodiment, by forming porous layers 30a, 30b made of hydrophobic oxide microparticles having the above-mentioned predetermined average primary particle diameter on at least one of the groove bottoms and groove walls of at least one of the grooves formed on the tread surface 14, it is possible to obtain the so-called lotus effect (an effect that exhibits the self-cleaning properties seen in plants of the Nelumbo nucifera family, and in this embodiment, this particularly refers to the water-repellent effect caused by the porous layer).

[0030] This lotus effect is achieved by the phenomenon that air trapped in the gaps between the hydrophobic oxide particles is initially pushed by the water, contracts, and then expands, causing the air to push the water back out of the porous layer. However, it should be noted that if the gaps between the hydrophobic oxide particles are too large, the water will pile up on the air to such an extent that the air cannot push back the water after the water pushes the air, and the lotus effect cannot be achieved.

[0031] More specifically, by setting the average primary particle diameter of the hydrophobic oxide fine particles to 3 nm or more, the gaps can be made to have a certain volume. As a result, when water gets into these gaps, the air compressed by the water is given a sufficient expansion force, so that the compressed air pushes back the water and pushes it out of the gaps, resulting in a lotus effect (water-repellent effect) that improves drainage performance.

[0032] In contrast, by setting the average primary particle diameter of the hydrophobic oxide microparticles to 100 nm or less, it is possible to prevent the gaps between the hydrophobic oxide microparticles from becoming excessively large, and to prevent the water from pushing the air and then becoming so large that the air cannot push it back. This allows water to be pushed out of the gaps, resulting in improved drainage performance due to the lotus effect (water-repellent effect).

[0033] The above effects are exerted at a higher level by setting the average primary particle diameter to 10 nm or more and 75 nm or less, and are exerted at a significantly higher level by setting the average primary particle diameter to 20 nm or more and 50 nm or less.

[0034] [Suitable example 1] In the tire described above, for example, the adhesion amount of the porous layer 30a to the groove bottom surface 17a and / or the groove wall surface 17b shown in FIG. 2 is 0.05 g / mm 2 More than 50g / m 2 It is preferable that the thickness of the porous layer 30a is 0.5 μm or more and 30 μm or less. This preferable embodiment also applies to the porous layer 30b formed on the groove bottom surface 23a and / or groove wall surface 23b shown in FIG. 3 (the same applies hereinafter). Here, the thickness of the porous layer 30a (30b) refers to the dimension of the porous layer 30a (30b) measured along the normal to the groove bottom surface 17a (23a) and the groove wall surface 17b (23b).

[0035] The amount of the porous layer 30a attached to the groove bottom surface 17a and / or the groove wall surface 17b is set to 0.05 g / mm 2 By setting the thickness of the porous layer 30a to 0.5 μm or more, the volume of the gaps between the hydrophobic oxide particles can be further increased. This allows more air to be trapped in the gaps, and when water hits the gaps, the air compressed by the water is given a greater expansion force. As a result, the compressed air pushes back the water more strongly, and the water can be pushed out of the gaps even more strongly, thereby achieving an even higher level of drainage performance due to the lotus effect (water-repellent effect).

[0036] In contrast, the amount of the porous layer 30a attached to the groove bottom surface 17a and / or the groove wall surface 17b is set to 50 g / mm 2 By setting the thickness of the porous layer 30a to 30 μm or less, the gaps between the hydrophobic oxide particles can be made even more compact. This makes it possible to more effectively prevent the water from pushing the air and then becoming so thick that the air cannot push it back. As a result, water can be more effectively pushed out of the gaps, and the drainage performance due to the lotus effect (water-repellent effect) can be achieved at an even higher level.

[0037] The inventors have found through numerous experiments that the water-repellent effect can only be achieved when both the adhesion amount and thickness of the porous layer are within the above-mentioned preferred ranges. In other words, the above-mentioned effect cannot be achieved even if only either the adhesion amount or thickness of the porous layer is within the above-mentioned preferred range. When the thickness of the porous layer is 0.5 μm or more and 30 μm or less, the porous layer is less likely to fall off from the tire groove surface (groove bottom surface and / or groove wall surface) when the tire rolls. This is because distortion occurs in the tire groove when the tire rolls, and if the thickness is not appropriate, the distortion can cause the porous layer to break and fall off easily.

[0038] The above-described effects are obtained when the amount of the porous layer 30a attached to the groove bottom surface 17a and / or the groove wall surface 17b is 0.5 g / mm 2 More than 45g / mm 2 The above-described effects are further enhanced by setting the adhesion amount of the porous layer 30a on the groove bottom surface 17a and / or the groove wall surface 17b to 5 g / mm or less, and by setting the thickness of the porous layer 30a to 0.75 μm or more and 25 μm or less. 2 More than 40g / mm 2 If the thickness of the porous layer 30a is set to 1.0 μm or more and 20 μm or less, an even higher level of performance can be achieved.

[0039] To prevent the porous layer from falling off the tire groove surface during tire rolling, the roughness of the tire groove surface is preferably within a predetermined range. The roughness of the tire groove surface (arithmetic mean roughness ra) is preferably set to 10 μm or more and 100 μm or less, because this allows the porous layer to be stably maintained even during tire rolling, thereby achieving improved drainage performance due to the lotus effect over a long period of time.

[0040] [Preferable example 2] In the tire of this embodiment, the specific surface area of ​​the porous layer shown in FIGS. 2 and 3 measured by the BET method is 50 m 2 / g or more 300m 2 / g or less. The BET method is a calculation method for measuring the surface area of ​​a porous body or the like, and specifically, is a specific surface area measurement method based on the BET adsorption theory, which is an extension of the monomolecular adsorption theory proposed by Langmuir by Brunauer, Emmett, Teller, et al., to the multimolecular layer adsorption theory, in which gas molecules (whose surface area is known) are adsorbed at low temperatures and the amount of adsorption is measured to calculate the surface area of ​​a porous body or the like.

[0041] Specific surface area means the surface area per unit mass of an object, and is mainly used to describe the surface area of ​​porous bodies such as catalysts. A large specific surface area means large voids, but it also means that the porous body has an unstable and brittle structure.

[0042] The specific surface area of ​​the porous layer measured by the BET method is 50 m 2 / g or more, the volume of the gaps between the hydrophobic oxide particles can be further increased. This allows more air to be trapped in the gaps, and when water hits these gaps, the air compressed by the water is given an even greater expansion force. As a result, the compressed air pushes back the water even more forcefully, and the water can be pushed out of the gaps even more forcefully, thereby achieving an even higher level of drainage performance due to the lotus effect (water-repellent effect).

[0043] In contrast, the specific surface area of ​​the porous layer measured by the BET method is 300 m 2 By setting the density to 0.1 / g or less, the gaps between the hydrophobic oxide particles can be made even more compact. This makes it possible to more effectively prevent the water from pushing the air and then getting on top of the air to such an extent that the air cannot push it back. As a result, water can be more effectively pushed out of the gaps, and the drainage performance due to the lotus effect (water-repellent effect) can be achieved at an even higher level.

[0044] The above effects were achieved when the specific surface area of ​​the porous layer measured by the BET method was increased to 75 m 2 / g or more 290m 2 / g or less, an even higher level of performance is achieved, and the specific surface area of ​​the porous layer measured by the BET method is 100m 2 / g or more 280m 2 / g or less, it can be performed at an extremely high level.

[0045] [Suitable example 3] In the tire of this embodiment, the material of the hydrophobic oxide particles constituting the porous layer is not particularly limited, and alumina, silica, titania, etc. can be used, but it is particularly preferable to use hydrophobic silica (silica modified with a hydrophobic group). By using hydrophobic silica as the hydrophobic oxide particles, it is possible to impart higher water repellency to the porous layer and further improve drainage performance.

[0046] It is more preferable to use hydrophobic silica having trimethylsilyl groups on its surface as the hydrophobic silica. Trimethylsilyl groups have low polarity and high lipophilicity, and therefore have high water repellency, making them suitable for use as the terminal structure of hydrophobic silica.

[0047] [Preferable example 4] In the tire of this embodiment, a primer layer is preferably formed between the groove bottom 17a (23a) and / or groove wall 17b (23b) and the porous layer 30a (30b) shown in Fig. 2 (Fig. 3). Here, the primer layer refers to an undercoat layer (adhesive layer) used when forming a porous layer on the groove surface (groove bottom surface and / or groove wall surface), and serves to stably hold the porous layer on the groove surface, particularly during tire rolling.

[0048] Unlike when a porous layer is formed directly on the groove surface, by interposing a primer layer between the groove surface and the porous layer, the hydrophobic oxide fine particles can be formed more uniformly over the entire area where the porous layer is formed. This makes it possible to suppress the detachment of the hydrophobic oxide fine particles from the tire surface due to repeated deformation of the tire while the vehicle is running, not just when the tire is new, and allows the above-mentioned lotus effect to be exerted for a longer period of time, thereby enabling excellent drainage performance to be exhibited for a long period of time.

[0049] The primer layer may be made of a resin film, such as a stretched polypropylene film, a non-stretched polypropylene film, a stretched nylon film, a high-density polyethylene film, a low-density polyethylene film, a linear low-density polyethylene film, or a polyethylene terephthalate film.

[0050] Since such a primer layer is a component formed for the purpose of stably holding the porous layer on the tire surface, it does not need to be thick. For this reason, it is preferable that the thickness of the primer layer is smaller than the thickness of the porous layer. This prevents the primer layer from being unnecessarily thick, and allows the porous layer to be efficiently held on the tire surface.

[0051] [Preferable example 5] In the tire of this embodiment (shown in FIG. 1), the porous layer is formed at least in the circumferential main groove 16, and when the tread surface position is defined as the 0% depth position and the groove bottom position is defined as the 100% depth position, it is preferable that the porous layer is formed at least in the range from the 50% depth position to the 100% depth position. Note that the depth position refers to a position measured in the tire radial direction from the tire profile line (outer contour) in a case where there are no grooves, in a tire meridian cross section.

[0052] Fig. 4 is a meridian cross-sectional view of a tire showing a region where a porous layer is formed in the circumferential main groove shown in Fig. 2. In the left diagram of Fig. 4, a porous layer 30c is formed in a range A in the tire radial direction from a 50% depth position to a 100% depth position, and in the right diagram, a porous layer 30d is formed in a range B in the tire radial direction from a 0% depth position to a 100% depth position.

[0053] Both of these two examples shown in Figure 4 are preferred forms because the porous layer is formed in at least a tire radial range A from the 50% depth position to the 100% depth position, but an intermediate example between these two examples (for example, an example in which the porous layer is formed in a range from the 25% depth position to the 100% depth position) is also included in the preferred examples.

[0054] Preferred Example 5 is significant in that it enables the aforementioned lotus effect to be obtained on the groove surface not only when the tire is new, but also particularly when the tire is in the final stages of use. Note that, as long as the porous layer is formed in a range A in the tire radial direction from the 50% depth position to the 100% depth position, the range in which the porous layer is formed may vary in the tire circumferential direction. That is, the outermost position in the tire radial direction of the porous layer may be varied in the tire circumferential direction while being maintained at a position radially outward of the 50% depth position.

[0055] [Suitable example 6] In the tire of this embodiment (shown in FIG. 1), the porous layer is preferably formed in main grooves that are formed in a region that occupies the central 50% of the tire's developed width. In this specification, the tire's developed width refers to the tire widthwise dimension between the tread ends when the tread is developed flat. Furthermore, the main groove is a groove in which a wear indicator is usually engraved, and in this specification, refers to a recessed portion that is 5 mm or more wide and 5 mm or more deep. This is not limited to circumferential main grooves that extend in the circumferential direction, but also includes lateral grooves that extend in the tire width direction and inclined grooves that are inclined relative to the tire width direction.

[0056] In preferred example 6, the target circumferential main groove does not need to be a main groove formed in the central 50% region of the tire developed width. In other words, it is sufficient that at least a portion of the target circumferential main groove is included in the central 50% region of the tire developed width.

[0057] In this way, at least a portion of the circumferential main groove (where the porous layer is formed) is included in an area that is likely to contribute to drainage performance, i.e., the central 50% area of ​​the tire developed width, thereby efficiently exerting the lotus effect and further improving drainage performance.

[0058] The effects described above are achieved to an even greater extent when the porous layer is formed in the main grooves formed in the central 40% region of the tire's developed width, and are achieved to an even greater extent when the porous layer is formed in the main grooves formed in the central 30% region of the tire's developed width.

[0059] (Specific Example 1 of Preferred Example 6) Fig. 5 is a plan view showing a suitable region for forming a porous layer in an example of a tread pattern of a tire according to this embodiment. Note that in Fig. 5, only components necessary for the following description are labeled with reference numerals.

[0060] In the tire 32 shown in Fig. 5, the entire regions of the circumferential main grooves 34a, 34b are included in the central 50% region (50% TDW) of the tire developed width TDW. These circumferential main grooves 34a, 34b are close to the tire width direction contact center (tire equatorial plane CP), and therefore contribute significantly to drainage performance. Therefore, by forming the porous layer specified in this embodiment in at least a portion of the main grooves formed in this region (50% TDW), drainage performance can be efficiently exhibited and further improved by the lotus effect.

[0061] 5, in each of the circumferential main grooves 34c and 34d, a portion of the region in the tire width direction is outside the central 50% region of the tire developed width TDW (50% TDW). However, even when only a specific region in the tire width direction is included within 50% TDW in this way, the lotus effect can be efficiently exerted, further improving drainage performance.

[0062] (Specific Example 2 of Preferred Example 6) Fig. 6 is a plan view showing a suitable formation region of a porous layer in a tire having a tread pattern different from that of the tire shown in Fig. 5. In the tire 40 shown in Fig. 6, a tread surface 44 formed in a tread portion 42 is formed with one circumferential main groove 46, bent grooves 48 (48a, 48b) extending in a serpentine manner in the tire circumferential direction on both outer sides in the tire width direction of the bent groove 46, branch grooves 50 (50a, 50b) extending from the bent groove 48 outward in the tire width direction, and lug grooves 52 (52a, 52b) located between adjacent branch grooves in the tire circumferential direction.

[0063] 6, the entire area of ​​the circumferential main groove 46 is included in the central 50% area (50% TDW) of the tire developed width TDW. Similarly, a portion of the bent grooves 48a, 48b is also included in the central 50% area (50% TDW) of the tire developed width TDW. The circumferential main groove 46 and the bent grooves 48a, 48b all correspond to the main groove defined in this embodiment.

[0064] In the example shown in FIG. 6, the porous layer specified in this embodiment is formed in the grooves 46, 48a, 48b, at least a portion of which is included in the tire width direction in a specific region (50% TDW), thereby efficiently exerting the lotus effect and further improving drainage performance.

[0065] <Tire manufacturing method> Next, a method for manufacturing the tire of this embodiment will be described. The tire of this embodiment is obtained through a tire material mixing step, a tire material processing step, a green tire molding step, a vulcanization step, a post-vulcanization inspection step, etc., as well as through a porous layer forming step of forming the porous layer described above on at least one of the groove bottom and the groove wall. When manufacturing the tire of this embodiment, the porous layer can be formed particularly in the following manner.

[0066] That is, the hydrophobic oxide microparticles that make up the porous layer described above are mixed with an organic solvent that is volatile at room temperature, and the mixture is applied manually or with an applicator to predetermined locations on the tire surface (groove bottoms and / or groove walls), thereby forming a porous layer on at least one of the groove bottoms and groove walls.

[0067] In forming the porous layer, as described above, alumina, hydrophobic silica, titania, ceria, etc. can be used as the hydrophobic oxide fine particles, and toluene, benzene, chlorofluorocarbons, cyclomethane, etc. can be used as the organic solvent.

[0068] Furthermore, when a primer layer is formed between the groove surface and the porous layer, the resin film is mixed with an organic solvent that is volatile at room temperature, and the mixture is applied to predetermined locations on the tire surface (groove bottom and / or groove wall) to form a primer layer (adhesive layer) on at least one of the groove bottom and groove wall, and then the above-mentioned porous layer is formed on the primer layer.

[0069] In forming the primer layer, as described above, a stretched polypropylene film or the like can be used as the hydrophobic oxide fine particles, and toluene, benzene, chlorofluorocarbons, cyclomethane, or the like can be used as the organic solvent.

[0070] In the tire manufactured as described above, the above-mentioned predetermined porous layer is formed on the groove surface (at least one of the groove bottom and groove wall), so that the so-called lotus effect can be exerted on the groove surface, and thus drainage performance can be exerted at a high level. [Example]

[0071] Tires of the Reference Example, Comparative Examples, and Invention Examples were manufactured with a tire size of 245 / 45R18 96W (specified by JATMA), a common tread pattern shown in Fig. 1, and common groove shapes shown in Figs. 2 and 3, and satisfying the conditions shown in Table 1. Note that the terms in Table 1 are all equivalent to the terms explained in this embodiment, and the descriptions thereof are partially simplified.

[0072] Next, each test tire (Reference Example, Comparative Example, and Inventive Example) was mounted on a rim of 18x9J size, and the air pressure of both the front and rear wheels was set to 240 kPa. These were then mounted on a rear-wheel drive vehicle (FR vehicle) with an engine displacement of 3000 cc. The hydroplaning occurrence speed of all these test tires was measured according to the following procedure.

[0073] (Method for assessing the speed at which hydroplaning occurs) A driving test was conducted in which the above vehicle equipped with each test tire was driven on a straight road into a pool of water 10 mm deep, and the entry speed into the pool was gradually increased to measure the limit speed at which hydroplaning occurred. The evaluation results were expressed as an index, with the reference example being set at 100. The higher the index value, the better the drainage performance.

[0074] [Table 1-1] [Table 1-2]

[0075] Table 1 shows that each of the tires of the invention examples, which fall within the technical scope of the present invention (i.e., a porous layer formed of hydrophobic oxide microparticles stacked in a three-dimensional network pattern on at least one of the groove bottom and groove wall of at least one of the grooves, and the average primary particle diameter of the hydrophobic oxide microparticles is 3 nm or more and 100 nm or less), achieves superior wet performance compared to the tires of the reference examples and comparative examples, which do not fall within the technical scope of the present invention. [Explanation of symbols]

[0076] 10, 32, 40 tires 12, 42 Tread section 14, 44 Tread surface 16, 34, 46 Circumferential main groove 17, 23 groove surface 17a, 23a groove bottom surface 17b, 23b Groove wall surface 18 Circumferential minor groove 20 Slant groove 22, 52 lug groove 24 Small ditch 26 Decorative groove 28 sipes 30a, 30b, 30c, 30d porous layer 48 Bend groove 50 Branch groove A, B Tire radial range CP tire equatorial plane Dc Circumferential direction of tire Dr Tire radial direction Dw Tire width direction TDW Tire development width

Claims

1. A tire having a plurality of grooves on the tread surface, A tire characterized in that a porous layer formed by laminating hydrophobic oxide fine particles in a three-dimensional network pattern is formed on at least one of the groove bottom and groove wall of at least one of the grooves, and the hydrophobic oxide fine particles have an average primary particle diameter of 3 nm or more and 100 nm or less.

2. The amount of the porous layer attached to the groove bottom surface and / or the groove wall surface is 0.05 g / mm ２ 50g / m or more ２ 2. The tire according to claim 1, wherein the porous layer has a thickness of 0.5 μm or more and 30 μm or less.

3. The specific surface area of ​​the porous layer measured by the BET method is 50 m ２ / g or more 300m ２ The tire according to claim 1 or 2, wherein the tensile strength is 1 / g or less.

4. 3. The tire according to claim 1, wherein the hydrophobic oxide fine particles are hydrophobic silica.

5. 5. The tire according to claim 4, wherein the hydrophobic silica has trimethylsilyl groups on its surface.

6. The tire according to claim 1 or 2, wherein a primer layer is formed between the groove bottom and / or the groove wall and the porous layer.

7. the porous layer is formed at least in the circumferential main groove, 3. The tire according to claim 1, wherein, when a tread surface position is defined as a 0% depth position and a groove bottom position is defined as a 100% depth position, the porous layer is formed at least in a range from a 50% depth position to a 100% depth position.

8. The tire according to claim 1 or 2, wherein the porous layer is formed in a main groove formed in a region that occupies a central 50% of the developed width of the tire.

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