Patent Application
20190168542
The present disclosure relates to a pneumatic tire.
From the standpoint of improving driving safety of automobiles, it is important to improve the steering stability of tires on dry and wet road surfaces. On the other hand, increased concern for environmental issues has led to a global movement towards regulating carbon dioxide emissions.
While improving the steering stability on dry and wet road surfaces, tire development must now also take into consideration high fuel efficiency, and therefore tire rolling resistance.
In this regard, JP 2012-92179 A (patent literature (PTL) 1) proposes a rubber composition that can improve the dry gripping performance and wet gripping performance of a tire and increase fuel efficiency. This rubber composition includes a rubber component (A) including natural rubber and/or synthetic isoprene rubber, a resin composition (B) including a novolac-type resorcinol resin and a resol-type phenolic resin, and a thermoplastic resin (C) that is immiscible with the rubber component (A).
Furthermore, J P 2014-9324 A (PTL 2) proposes a rubber composition that can improve the braking performance of the tire on wet road surfaces and increase fuel efficiency. In this rubber composition, the temperature at the peak position of the tan δ temperature curve is within a specific range, tan δ at 0° C. is 0.95 or higher, and tan δ at −5° C. and tan δ at 5° C. satisfy a specific relationship.
PTL 1: JP 2012-92179 A
PTL 2: JP 2014-9324 A
However, there is typically a trade-off between the steering stability and rolling resistance of a tire. For example, improving the steering stability on dry and wet road surfaces worsens the rolling resistance, whereas reducing the rolling resistance worsens the steering stability on dry and wet road surfaces.
Furthermore, the steering stability on dry and wet road surfaces cannot be greatly improved without worsening of the rolling resistance of the tire even when using the rubber compositions of PTL 1 and PTL 2.
To resolve this technical problem, the present disclosure provides a pneumatic tire that can greatly improve the steering stability on dry and wet road surfaces without worsening of the rolling resistance.
The main features of the present disclosure for resolving the above problem are as follows.
A pneumatic tire according to the present disclosure includes lug grooves and widthwise sipes on a surface of a tread;
a rubber composition used in the tread includes a rubber component (A) including 50 mass % or more of at least one type of isoprene-based rubber selected from the group consisting of natural rubber and synthetic isoprene rubber, a thermoplastic resin (B), and a filler (C) including 70 mass % or more of silica, the amount of the thermoplastic resin (B) is 5 to 40 parts by mass per 100 parts by mass of the rubber component (A), and in the rubber composition, tan δ at 0° C. is 0.5 or less, the difference between tan δ at 30° C. and tan δ at 60° C. is 0.070 or less, and the storage modulus at a dynamic strain of 1% and 0° C. is 20 MPa or less; and a tread edge component ratio of the tread as defined by Expression (1) is 6.0 to 8.0;
tread edge component ratio=(sum of tire widthwise extending length of the lug grooves and tire widthwise extending length of the widthwise sipes on the surface of the tread)/(tire circumferential length). Expression (1):
This pneumatic tire greatly improves the steering stability on dry and wet road surfaces without worsening of the rolling resistance.
In the present disclosure, a lug groove refers to a groove with a groove width (opening width to the tread surface) greater than 1.5 mm, whereas a widthwise sipe refers to a groove with a groove width (opening width to the tread surface) equal to or less than 1.5 mm. Both types of grooves extend in a direction other than the tire circumferential direction to form tread edges with respect to the tire circumferential direction.
Also, the tread surface in the present disclosure refers to the peripheral surface, over the entire circumference of the tire, that comes into contact with the road surface when a tire assembled with an applicable rim and filled to a prescribed internal pressure is rolled while having a load corresponding to the maximum load capability applied thereon.
The “applicable rim” refers to a standard rim of an applicable size, such as the Measuring Rim in the STANDARDS MANUAL of the European Tire and Rim Technological Organization (ETRTO) in Europe or the Design Rim in the YEAR BOOK of the Tire and Rim Association, Inc. (TRA) in the USA, that is described in industrial standards effective in the region where the tire is manufactured and used, such as the JATMA YEAR BOOK published by the Japan Automobile Tyre Manufacturers Association (JATMA) in Japan, the STANDARDS MANUAL of the ETRTO, and the YEAR BOOK of the TRA.
The “prescribed internal pressure” represents the air pressure corresponding to the maximum load capability for each applicable size and ply rating prescribed by the aforementioned JATMA YEAR BOOK and the like. The “maximum load capability” represents the maximum mass, under the aforementioned standards, permitted to be loaded on the tire.
In the present disclosure, the tire widthwise extending length of a lug groove that extends on the tread surface refers to the projected length of the lug groove in the tire width direction. The tire widthwise extending length of a widthwise sipe that extends on the tread surface refers to the projected length of the widthwise sipe in the tire width direction.
In the present disclosure, the tire circumferential length refers to the circumferential length of the tread surface at the tire equatorial plane.
In the pneumatic tire of the present disclosure, the difference between tan δ at 0° C. and tan δ at 30° C. is preferably 0.30 or less in the rubber composition. This can reduce the temperature dependence of the rolling resistance of the tire.
In the pneumatic tire of the present disclosure, the difference between tan δ at 0° C. and tan δ at 60° C. is preferably 0.35 or less in the rubber composition. In this case as well, the temperature dependence of the rolling resistance of the tire can be reduced.
In a preferred example of the pneumatic tire of the present disclosure, the rubber composition further includes 1 to 5 parts by mass of a softener (D) per 100 parts by mass of the rubber component (A). This can sufficiently ensure the rigidity of the tread while facilitating kneading of the rubber composition.
The softener (D) is preferably a mineral-derived or petroleum-derived softener. This further facilitates kneading of the rubber composition.
In another preferred example of the pneumatic tire of the present disclosure, the amount of the silica in the rubber composition is 40 to 70 parts by mass per 100 parts by mass of the rubber component (A). This can further improve the steering stability of the tire on dry and wet road surfaces while reducing the rolling resistance of the tire.
In another preferred example of the pneumatic tire of the present disclosure, the filler (C) further includes carbon black, and the amount of the carbon black is 1 to 10 parts by mass per 100 parts by mass of the rubber component (A). This further improves the steering stability of the tire on dry and wet road surfaces.
In another preferred example of the pneumatic tire of the present disclosure, the thermoplastic resin (B) is one or more kinds of resins selected from the group consisting of C5-based resins, C9-based resins, C5/C9-based resins, dicyclopentadiene resins, rosin resins, alkyl phenolic resins, and terpene phenolic resins. In this case as well, the steering stability of the tire on dry and wet road surfaces is further improved.
In the tread of the pneumatic tire of the present disclosure, an edge component ratio of a tread center portion defined by Expression (2) below is preferably higher than an edge component ratio of tread shoulder portions defined by Expression (3) below;
edge component ratio of tread center portion=(sum of tire widthwise extending length of the lug grooves and tire widthwise extending length of the widthwise sipes in the tread center portion)/(tire circumferential length); Expression (2):
edge component ratio of tread shoulder portions=(sum of tire widthwise extending length of the lug grooves and tire widthwise extending length of the widthwise sipes in the tread shoulder portions)/(tire circumferential length). Expression (3):
This can greatly improve the steering stability of the tire on dry and wet road surfaces while suppressing wear of the tread shoulder portions.
Here, the tread center portion refers to the ½ portion of the tire tread surface located at the tire width direction center when the tread surface is divided into four even parts in the tire width direction along planes parallel to the equatorial plane. The tread shoulder portions refer to a pair of ¼ portions of the tire tread surface located at the outer sides in the tire width direction when the tread surface is divided into four even parts in the tire width direction along planes parallel to the equatorial plane. Accordingly, the tread edge component ratio defined in Expression (1) is the sum of the edge component ratio of the tread center portion defined in Expression (2) and the edge component ratio of the tread shoulder portions defined in Expression (3).
The present disclosure can provide a pneumatic tire that can greatly improve the steering stability on dry and wet road surfaces without worsening of the rolling resistance.
In the accompanying drawings:
The pneumatic tire of the present disclosure is described below in detail with reference to embodiments thereof.
The lug grooves 12a to 12f and the widthwise sipes 13a to 13h that extend at an inclination relative to the tire circumferential direction C are preferably inclined from 30° to 85°, more preferably 40° to 85°, relative to the tire circumferential direction C.
In the present disclosure, the tire widthwise extending length of a lug groove refers to the projected length of the lug groove in the tire width direction, and the tire widthwise extending length of a widthwise sipe refers to the projected length of the widthwise sipe in the tire width direction, as described above. For example, on the tread 10 of the pneumatic tire illustrated in
In the tread of the pneumatic tire according to the present disclosure, the tread edge component ratio defined by Expression (1), i.e. the sum of the tire widthwise extending length of the lug grooves and tire widthwise extending length of the widthwise sipes on the tread surface divided by the tire circumferential length (i.e. the circumferential length of the tread surface at the tire equatorial plane E), is 6.0 to 8.0. Deformation of the tread decreases and strain decreases when the tread edge component ratio defined by Expression (1) is less than 6.0. Consequently, the effects of the below-described rubber composition used in the tread are not sufficiently achieved, and the steering stability of the tire on dry and wet road surfaces cannot be sufficiently improved. On the other hand, the contact area with the contact patch of the land portions of the tread decreases when the tread edge component ratio defined by Expression (1) exceeds 8.0. In this case as well, the effects of the below-described rubber composition used in the tread are not sufficiently achieved, and the steering stability of the tire on dry and wet road surfaces cannot be sufficiently improved.
Here, the tread edge component ratio defined by Expression (1) is preferably in a range of 7.0 to 8.0 to further achieve the effects of the rubber composition used in the tread.
Similarly, the edge component ratio derived from the lug grooves (i.e., the sum of the tire widthwise extending length of the lug grooves on the tread surface divided by the tire circumferential length) is preferably in a range of 3.0 to 4.25, more preferably a range of 3.5 to 4.0, and the edge component ratio derived from the widthwise sipes (i.e. the sum of the tire widthwise extending length of the widthwise sipes on the tread surface divided by the tire circumferential length) is preferably in a range of 3.0 to 4.25, more preferably a range of 3.5 to 4.0, to further achieve the effects of the rubber composition used in the tread.
In the tread 10 of the pneumatic tire illustrated in
In the present disclosure, as described above, the tread center portion 14 refers to the ½ portion of the tire tread surface located at the tire width direction center when the tread surface is divided into four even parts in the tire width direction along planes parallel to the equatorial plane E. In other words, the tread center portion 14 is the central ½ range of the width (periphery width) W of the tread surface in the tire width direction, centered on the tire equatorial plane E (i.e. a ¼ W range on either side of the tire equatorial plane E in the tire width direction). On the other hand, the tread shoulder portions 15, 16 refer to a pair of ¼ portions of the tire tread surface located at the outer sides in the tire width direction when the tread surface is divided into four even parts in the tire width direction along planes parallel to the equatorial plane E. In other words, the tread shoulder portions 15, 16 are the ¼ ranges of the width W of the tread surface in the tire width direction, located at either outer side of the tread center portion 14 in the tire width direction.
A rubber composition used in the tread 10 includes a rubber component (A) including 50 mass % or more of at least one type of isoprene-based rubber selected from the group consisting of natural rubber and synthetic isoprene rubber, a thermoplastic resin (B), and a filler (C) including 70 mass % or more of silica, and in the rubber composition, the amount of the thermoplastic resin (B) is 5 to 40 parts by mass per 100 parts by mass of the rubber component (A), tan δ at 0° C. is 0.5 or less, the difference between tan δ at 30° C. and tan δ at 60° C. is 0.070 or less, and the storage modulus (E′) at a dynamic strain of 1% and 0° C. is 20 MPa or less.
Adding a prescribed amount of the thermoplastic resin (B) to the rubber composition can reduce the elastic modulus in a high strain region while suppressing a reduction of the elastic modulus in a low strain region. Therefore, applying this rubber composition to a tire tread can ensure rigidity of the tread in a portion far from the contact patch with the road surface, where strain is small during running, while increasing the deformation volume of the tread near the contact patch with the road surface, where strain is large during running.
Setting the content ratio of silica in the filler (C) that is added to the rubber composition to 70 mass % or more can suppress a rise in tan δ (loss tangent) and suppress worsening of the rolling resistance of a tire with a tread in which the rubber composition is applied.
The coefficient of friction (μ) on dry and wet road surfaces is proportional to the product of rigidity of the entire tread, the amount of deformation of the tread, and tan δ (loss tangent). Hence, even if a rise in tan δ is suppressed to control worsening of the rolling resistance in the pneumatic tire of the present disclosure, in which the rubber composition is applied to the tread, the amount of deformation of the tread can be increased while ensuring rigidity of the entire tread, thereby sufficiently increasing the coefficient of friction (μ) on dry and wet road surfaces. This increase in the coefficient of friction (μ) on dry and wet road surfaces improves the steering stability on dry and wet road surfaces. In the tread of the pneumatic tire according to the present disclosure, the tread edge component ratio defined by Expression (1) is 6.0 to 8.0, deformation and strain of the tread are large, and the contact area with the tread contact patch is also large. Consequently, the effects of the rubber composition applied to the tread are sufficiently achieved.
The pneumatic tire of the present disclosure can therefore greatly improve the steering stability on dry and wet road surfaces while suppressing worsening of the rolling resistance.
In the rubber composition, tan δ at 0° C. is 0.5 or less, preferably 0.45 or less, and even more preferably 0.4 or less to suppress worsening of the rolling resistance. While no lower limit is placed on tan δ at 0° C., tan δ at 0° C. is normally 0.15 or more. The rolling resistance of the tire might worsen if tan δ at 0° C. in the rubber composition exceeds 0.5.
In the rubber composition, tan δ at 30° C. is preferably 0.4 or less, more preferably 0.35 or less, and is normally 0.1 or more. Furthermore, in the rubber composition, tan δ at 60° C. is preferably 0.35 or less, more preferably 0.3 or less, and is normally 0.05 or more. These ranges can further suppress worsening of the rolling resistance of the tire.
To reduce the temperature dependence of the rolling resistance, the difference between tan δ at 30° C. and tan δ at 60° C. in the rubber composition is 0.070 or less, preferably 0.060 or less, more preferably 0.055 or less, and even more preferably 0.050 or less. No lower limit is placed on the difference between tan δ at 30° C. and tan δ at 60° C., and this difference may be 0. If the difference between tan δ at 30° C. and tan δ at 60° C. in the rubber composition exceeds 0.070, the temperature dependence of the rolling resistance of the tire increases.
To reduce the temperature dependence of the rolling resistance, the difference between tan δ at 0° C. and tan δ at 30° C. in the rubber composition is preferably 0.30 or less, more preferably from 0.14 to 0.30, even more preferably 0.15 to 0.25, and particularly preferably 0.16 to 0.20.
To reduce the temperature dependence of the rolling resistance, the difference between tan δ at 0° C. and tan δ at 60° C. in the rubber composition is preferably 0.35 or less, more preferably 0.24 or less, and even more preferably 0.23 or less. This difference may also be 0.
From the standpoint of steering stability of the tire on wet road surfaces, the storage modulus (E′) of the rubber composition at a dynamic strain of 1% and 0° C. is 20 MPa or less, preferably 18 MPa or less, more preferably 16 MPa or less, and is preferably 3 MPa or more, more preferably 5 MPa or more. The rubber composition is highly flexible if the storage modulus at a dynamic strain of 1% and 0° C. is 20 MPa or less. Applying this rubber composition to a tire tread can improve the grounding property of the tread, greatly improving the steering stability of the tire on dry and wet road surfaces.
From the standpoint of steering stability of the tire on dry and wet road surfaces, the tensile strength (Tb) of the rubber composition is preferably 20 MPa or more, more preferably 23 MPa or more. Using a rubber composition with a tensile strength of 20 MPa or more in the tread improves the rigidity of the tread overall and further improves the steering stability on dry and wet road surfaces.
The rubber component (A) of the rubber composition includes 50 mass % or more of at least one type of isoprene-based rubber selected from the group consisting of natural rubber and synthetic isoprene rubber, preferably 60 mass % or more, and more preferably 70 mass % or more. No upper limit is placed on the content ratio of the isoprene-based rubber in the rubber component (A), and the entire rubber component (A) may be isoprene-based rubber. When the content ratio of the isoprene-based rubber in the rubber component (A) is 50 mass % or more, a rise in the tan δ (loss tangent) of the rubber composition is suppressed. Applying this rubber composition to a tire tread can suppress worsening of the rolling resistance of the tire.
Other than natural rubber (NR) and synthetic isoprene rubber (IR), the rubber component (A) may include synthetic diene rubber such as polybutadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), and styrene-isoprene copolymer rubber (SIR), or may include another synthetic rubber. One kind of these rubber components (A) may be used alone, or a blend of two or more kinds may be used.
The rubber composition includes the thermoplastic resin (B). Adding the thermoplastic resin (B) to the rubber composition can reduce the elastic modulus in a high strain region while suppressing a reduction of the elastic modulus in a low strain region. Therefore, applying the rubber composition that includes the thermoplastic resin (B) to a tire tread can ensure rigidity of the tread in a portion far from the contact patch with the road surface, where strain is small during running, while increasing the deformation volume of the tread near the contact patch with the road surface, where strain is large during running. Consequently, the friction coefficient (μ) at dry and wet road surfaces increases, which can improve the steering stability of the tire on dry and wet road surfaces.
The amount of the thermoplastic resin (B) is 5 to 40 parts by mass per 100 parts by mass of the rubber component (A), preferably 8 to 30 parts by mass, and more preferably 10 to 20 parts by mass. When the amount of the thermoplastic resin (B) is 5 parts by mass or more per 100 parts by mass of the rubber component (A), the elastic modulus of the rubber composition in the high strain region can be reduced, and when the amount is 40 parts by mass or less, a reduction of the elastic modulus of the rubber composition in the low strain region can be suppressed.
C5-based resins, C9-based resins, C5/C9-based resins, dicyclopentadiene resins, rosin resins, alkyl phenolic resins, and terpene phenolic resins are preferable as the thermoplastic resin (B) from the standpoint of steering stability of the tire on dry and wet road surfaces. One kind of these thermoplastic resins (B) may be used alone, or a combination of two or more kinds may be used.
The C5-based resins refer to C5-based synthetic petroleum resins. Examples of C5-based resins include aliphatic petroleum resins obtained by using a Friedel-Crafts catalyst such as AlCl3 or BF3 to polymerize a C5 fraction obtained by pyrolysis of naphtha in the petrochemical industry. The C5 fraction usually includes an olefinic hydrocarbon such as 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, or 3-methyl-1-butene, a diolefinic hydrocarbon such as 2-methyl-1,3-butadiene, 1,2-pentadiene, 1,3-pentadiene, or 3-methyl-1,2-butadiene, or the like. Commercial products may be used as the C5-based resins, such as the “Escorez® 1000 series”, which are aliphatic petroleum resins produced by ExxonMobil Chemical Company; “A100, B170, M100, R100” in the “Quintone® 100 series”, which are aliphatic petroleum resins produced by Zeon Corporation; and the like.
The C9-based resins are, for example, resins resulting from polymerization of an aromatic group that has 9 carbon atoms and has, as the principal monomers, vinyl toluene, alkyl styrene, and indene, which are C9 fraction by-products produced along with petrochemical raw materials, such as ethylene or propylene, by pyrolysis of naphtha in the petrochemical industry. Specific examples of C9 fractions obtained by pyrolysis of naphtha include vinyltoluene, α-methylstyrene, β-methylstyrene, γ-methylstyrene, o-methylstyrene, p-methylstyrene, vinyltoluene, and indene. Along with a C9 fraction, the C9-based resin may use a C8 fraction, such as styrene, a C10 fraction, such as methylindene or 1,3-dimethylstyrene, and other substances such as naphthalene, vinylnaphthalene, vinylanthracene, or p-tert-butylstyrene as raw materials. These C8-C10 fractions and the like may simply be mixed or may be co-polymerized using a Friedel-Crafts catalyst, for example. The C9-based resin may be a modified petroleum resin modified by a compound including a hydroxyl group, an unsaturated carboxylic acid compound, or the like. Commercial products may be used as the C9-based resins. Examples of an unmodified C9-based petroleum resin include “Neopolymer L-90”, “Neopolymer 120”, “Neopolymer 130”, and “Neopolymer 140” (produced by JX Nippon Oil & Energy Corporation), and the like.
The C5/C9-based resins refer to C5/C9-based synthetic petroleum resins. Examples of C5/C9-based resins include a solid polymer obtained by polymerizing a petroleum-derived C5 to C11 fraction using a Friedel-Crafts catalyst such as AlCl3 or BF3. Specific examples include copolymers having, as main components, styrene, vinyltoluene, a-methylstyrene, indene, and the like. As the C5/C9-based resins, resins with little C9 or higher component are preferable in terms of compatibility with the rubber component (A). Here, including “little C9 or higher component” means that the amount of C9 or higher component in the total amount of the resin is less than 50 mass %, preferably 40 mass % or less. Commercial products may be used as the C5/C9-based resins. Examples include “Quintone® G100B” (produced by Zeon Corporation) and “ECR213” (produced by ExxonMobil Chemical Company).
The dicyclopentadiene resin is a petroleum resin manufactured using dicyclopentadiene, which is obtainable by dimerization of cyclopentadiene, as the main raw material. Commercial products may be used as the dicyclopentadiene resin. Examples include “1105, 1325, 1340” in the “Quintone® 1000 series”, which are alicyclic petroleum resins produced by Zeon Corporation.
The rosin resins are natural resins that are the residue remaining after gathering a balsam such as rosin, which is the sap of a pinaceae plant, and distilling turpentine. The rosin resins have rosin acid (abietic acid, palustric acid, isopimaric acid, etc.) as the main component. The rosin resins may also be modified resins or hydrogenated resins produced by modifying, hydrogenating, etc. these natural resins. Examples include natural resin rosin, and polymerized rosins and partially hydrogenated rosins thereof; glycerin ester rosin, and partially hydrogenated rosins, completely hydrogenated rosins, and polymerized rosins thereof; and pentaerythritol ester rosin, and partially hydrogenated rosins and polymerized rosins thereof. Examples of natural resin rosins include gum rosin, tall oil rosin, and wood rosin included in raw rosin or tall oil. Commercial products may be used as the rosin resin. Examples include “Neotall 105” (produced by Harima Chemicals Group, Inc.), “SN-Tack 754” (produced by San Nopco Ltd.), “Lime Resin No. 1”, “Pensel A” and “Pensel AD” (produced by Arakawa Chemical Industries, Ltd.), “Polypale” and “Pentalyn C” (produced by Eastman Chemical Co.), and “Highrosin® S” (produced by Taishamatsu Essential Oil Co., Ltd.).
The alkyl phenolic resin may, for example, be obtained by a condensation reaction of an alkylphenol with formaldehyde in the presence of a catalyst. Commercial products may be used as the alkyl phenolic resin. Examples include “Hitanol 1502P” (produced by Hitachi Chemical Co., Ltd.), “Tackirol 201” (produced by Taoka Chemical Co., Ltd.), “Tackirol 250-I” (a brominated alkylphenol formaldehyde resin produced by Taoka Chemical Co., Ltd.), “Tackirol 250-111” (a brominated alkylphenol formaldehyde resin produced by Taoka Chemical Co., Ltd.), “R7521P”, “SP1068”, “R7510PJ”, “R7572P” and “R7578P” (produced by Schenectady Chemicals, Inc.), and “R7510PJ” (produced by SI GROUP INC).
The terpene phenolic resin may, for example, be obtained by reacting terpenes and various phenols using a Friedel-Crafts catalyst or by further condensing the resultant with formalin. While the terpenes used as raw material are not restricted, a monoterpene hydrocarbon such as α-pinene or limonene is preferable, a terpene including α-pinene is more preferable, and α-pinene itself is particularly preferable. Commercial products may be used as the terpene phenolic resin. Examples include “Tamanol 803L” and “Tamanol 901” (produced by Arakawa Chemical Industries, Ltd.), and “YS Polyster U” series, “YS Polyster T” series, “YS Polyster S” series, “YS Polyster G” series, “YS Polyster N” series, “YS Polyster K” series, and “YS Polyster TH” series (produced by Yasuhara Chemical Co., Ltd.).
The rubber composition includes the filler (C). The filler (C) includes 70 mass % or more of silica, preferably 80 mass % or more, and more preferably 90 mass % or more. No upper limit is placed on the ratio of silica in the filler (C), and the entire filler (C) may be silica. When the ratio of silica in the filler (C) is 70 mass % or higher, then tan δ of the rubber composition can be reduced, and worsening of the rolling resistance of the tire to which the rubber composition is applied can be suppressed.
Any type of silica may be used. Examples include wet silica (hydrous silicate), dry silica (anhydrous silicate), calcium silicate, and aluminum silicate. Among these, wet silica is preferred. One kind of these silicas may be used alone, or two or more kinds may be used in combination.
The amount of the silica in the rubber composition is preferably in a range of 40 to 70 parts by mass per 100 parts by mass of the rubber component (A), more preferably a range of 45 to 60 parts by mass. When the amount of the silica is 40 parts by mass or more per 100 parts by mass of the rubber component (A), tan δ of the rubber composition can be lowered, and the rolling resistance of a tire to which the rubber composition is applied can be reduced. When the amount of the silica is 70 parts by mass or less, the rubber composition is highly flexible. Applying this rubber composition to tread rubber of a tire increases the deformation volume of the tread rubber, allowing further improvement in the steering stability of the tire on dry and wet road surfaces.
In the rubber composition, the filler (C) preferably further includes carbon black. The amount of the carbon black is preferably in a range of 1 to 10 parts by mass per 100 parts by mass of the rubber component (A), more preferably a range of 3 to 8 parts by mass. Adding 1 part by mass or more of the carbon black can improve the rigidity of the rubber composition, and adding 10 parts by mass or less can suppress a rise in tan δ. Hence, applying this rubber composition to the tread rubber of a tire can further improve the steering stability on dry and wet road surfaces while suppressing worsening of the rolling resistance of the tire.
The carbon black is not restricted. Examples include GPF, FEF, HAF, ISAF, and SAF grade carbon black. Among these, ISAF and SAF grade carbon black are preferable for improving the steering stability of the tire on dry and wet road surfaces. One kind of these carbon blacks may be used alone, or two or more kinds may be used in combination.
In addition to the above-described silica and carbon black, the filler (C) may also include aluminum hydroxide, alumina, clay, calcium carbonate, or the like.
The amount of the filler (C) in the rubber composition is preferably 30 to 100 parts by mass, more preferably 40 to 80 parts by mass, per 100 parts by mass of the rubber component (A). When the amount of the filler (C) in the rubber composition is within the aforementioned ranges, then applying the rubber composition to a tire tread can further improve the steering stability on dry and wet road surfaces while reducing the rolling resistance of the tire.
From the standpoint of processability and operability, the rubber composition can further include a softener (D). The amount of the softener (D) is preferably in a range of 1 to 5 parts by mass per 100 parts by mass of the rubber component (A), more preferably a range of 1.5 to 3 parts by mass. Adding 1 part by mass or more of the softener (D) facilitates kneading of the rubber composition, whereas adding 5 parts by mass or less of the softener (D) can suppress a reduction in the rigidity of the tread.
Examples of the softener (D) include mineral-derived oil, petroleum-derived aromatic oil, paraffin oil, naphthene oil, and palm oil derived from natural products. Among these, a mineral-derived softener and a petroleum-derived softener are preferred from the standpoint of steering stability of the tire on dry and wet road surfaces.
To improve the effect of adding silica, a silane coupling agent is preferably added to the rubber composition. Any silane coupling agent may be added. Examples include bis(3-triethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylpropyl) trisulfide, bis(3-triethoxysilylpropyl) disulfide, bis(2-triethoxysilylethyl) tetrasulfide, bis(3-trimethoxysilylpropyl) tetrasulfide, bis(2-trimethoxysilylethyl) tetrasulfide, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl benzothiazolyl tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, bis(3-diethoxymethylsilylpropyl) tetrasulfide, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, and dimethoxymethylsilylpropyl benzothiazolyl tetrasulfide. One kind of these silane coupling agents may be used alone, or two or more kinds may be used in combination.
The amount of the silane coupling agent is preferably in a range of 2 to 20 parts by mass per 100 parts by mass of the silica, more preferably a range of 5 to 15 parts by mass. When the amount of the silane coupling agent is 2 parts by mass or more per 100 parts by mass of the silica, the effect of adding the silica is sufficiently improved. When the amount of the silane coupling agent is 20 parts by mass or less per 100 parts by mass of the silica, gelation of the rubber component (A) is unlikely.
The rubber composition preferably further includes a fatty acid metal salt. Examples of the metal useable in the fatty acid metal salt include Zn, K, Ca, Na, Mg, Co, Ni, Ba, Fe, Al, Cu, and Mn, with Zn being preferable. Examples of the fatty acid usable in the fatty acid metal salt include fatty acids having a saturated or unsaturated linear, branched, or cyclic structure with 4 to 30 carbon atoms, or mixtures thereof. Among these, saturated or unsaturated linear fatty acids having 10 to 22 carbon atoms are preferable. Examples of saturated linear fatty acids having 10 to 22 carbon atoms include lauric acid, myristic acid, palmitic acid, and stearic acid. Examples of unsaturated linear fatty acids having 10 to 22 carbon atoms include oleic acid, linoleic acid, linolenic acid, and arachidonic acid. One kind of fatty acid metal salt may be used alone, or a combination of two or more kinds may be used.
The amount of the fatty acid metal salt is preferably in a range of 0.1 to 10 parts by mass per 100 parts by mass of the rubber component (A), more preferably a range of 0.5 to 5 parts by mass.
In addition to the rubber component (A), the thermoplastic resin (B), the filler (C), the softener (D), the silane coupling agent, and the fatty acid metal salt, the rubber composition may also include compounding agents typically used in the rubber industry. For example, stearic acid, an age resistor, zinc oxide (zinc white), a vulcanization accelerator, a vulcanizing agent, or the like may be appropriately selected and added in a range that does not impede the object of the present disclosure. Commercially available products may be suitably used as these additives. However, to reduce the storage modulus (E′) of the rubber composition at a dynamic strain of 1% and 0° C., a thermosetting resin such as a novolac-type or resol-type phenolic resin, a resorcin resin, or the like is preferably not added.
The rubber composition is preferably produced through a process of kneading the following, excluding a vulcanization compounding agent that includes a vulcanizing agent and a vulcanization accelerator, at 150° C. to 165° C.: a rubber component (A) that contains 50 mass % or more of at least one type of isoprene-based rubber selected from the group consisting of natural rubber and synthetic isoprene rubber, a thermoplastic resin (B), and a filler (C) including 70 mass % or more of the silica.
Kneading at 150° C. to 165° C. while excluding the vulcanization compounding agent can disperse compounding agents other than the vulcanization compounding agent in the rubber component (A) uniformly while avoiding premature vulcanization (scorching). This allows the effects of each compounding agent to be sufficiently achieved and can reduce the difference between tan δ at 30° C. and tan δ at 60° C. while reducing tan δ at 0° C. in the rubber composition.
The value of tan δ of the rubber composition, the difference between tan δ at various temperatures, the storage modulus (E′), and the tensile strength (Tb) can be changed by adjusting not only the above-described kneading temperature, but also the type and blend ratio of the rubber component (A), the type and amount of the thermoplastic resin (B), the silica content in the filler (C), the type of silica, and the like, and also the type and amount of other compounding agents.
During production of the rubber composition, kneading may be performed again at a different temperature lower than 150° C. after kneading at 150° C. to 165° C. as described above.
During production of the rubber composition, a vulcanization compounding agent that includes a vulcanizing agent and a vulcanization accelerator is preferably added after the compounding agents other than the vulcanization compounding agent are sufficiently dispersed in the rubber component (A). Kneading is then preferably performed at a temperature that can prevent premature vulcanization (scorching), such as 90° C. to 120° C.
The kneading time during kneading at each temperature during production of the rubber composition is not restricted and may be set appropriately considering factors such as the size of the kneading device, the volume of the raw material, and the type and state of the raw material.
Examples of the vulcanizing agent include sulfur.
The amount of the vulcanizing agent is preferably in a range of 0.1 to 10 parts by mass as sulfur per 100 parts by mass of the rubber component (A), more preferably a range of 1 to 4 parts by mass. When the amount of the vulcanizing agent is 0.1 parts by mass or more as sulfur, the fracture strength, wear resistance, and the like of the vulcanized rubber can be ensured. When this amount is 10 parts by mass or less, the rubber elasticity can be sufficiently ensured. In particular, setting the amount of the vulcanizing agent to 4 parts by mass or less as sulfur can further improve the steering stability of the tire on dry and wet road surfaces.
Any vulcanization accelerator may be used. Examples include a thiazole type vulcanization accelerator such as 2-mercaptobenzothiazole (M), dibenzothiazolyl disulfide (DM), N-cyclohexyl-2-benzothiazolyl sulfenamide (CZ), and N-tert-butyl-2-benzothiazolyl sulfenamide (NS); and a guanidine type vulcanization accelerator such as 1,3-diphenyl guanidine (DPG). The rubber composition preferably includes three types of vulcanization accelerators.
The amount of the vulcanization accelerator is preferably in a range of 0.1 to 5 parts by mass per 100 parts by mass of the rubber component (A), more preferably a range of 0.2 to 3 parts by mass.
The rubber composition may be produced using a Banbury mixer, a roll, or the like, for example, to blend and knead the above-described components, i.e. the rubber component (A), the thermoplastic resin (B), the filler (C), and any compounding agents selected as necessary, and then subjecting the result to processes such as warming and extrusion.
In accordance with the type of applicable tire, the pneumatic tire of the present disclosure may be obtained by first molding a tire using an unvulcanized rubber composition and then vulcanizing the tire, or by first molding a tire using semi-vulcanized rubber yielded by a preliminary vulcanization process and then fully vulcanizing the tire. The members other than the tread in the pneumatic tire of the present disclosure are not restricted, and widely-known members may be used. The pneumatic tire of the present disclosure may be filled with ordinary air or air with an adjusted partial pressure of oxygen, or the pneumatic tire may be filled with an inert gas such as nitrogen, argon, or helium.
The present disclosure is described below in detail with reference to Examples. However, the present disclosure is no way limited to the following Examples.
<Preparation and Measurement of Properties of Rubber Composition>
Rubber compositions with the formulations listed in Table 1 were prepared, and the loss tangent (tan δ), storage modulus (E′), and tensile strength (Tb) of the resulting rubber compositions were measured with the following methods. Table 1 lists the results.
(1) Loss Tangent (Tan δ) and Storage Modulus (E′)
The loss tangent (tan δ) at 0° C., 30° C., and 60° C. and the storage modulus (E′) at 0° C. of vulcanized rubber obtained by vulcanizing the rubber compositions at 145° C. for 33 minutes were measured under the conditions of an initial strain of 2%, a dynamic strain of 1%, and a frequency of 52 Hz, using a spectrometer produced by Ueshima Seisakusho Co., Ltd.
(2) Tensile Strength (Tb)
The tensile strength (Tb) of vulcanized rubber obtained by vulcanizing the rubber composition at 145° C. for 33 minutes was measured in accordance with JIS K6251-1993.
<Modified Styrene-Butadiene Rubber 1>
In an 800 mL pressure-resistant glass vessel that had been dried and purged with nitrogen, a cyclohexane solution of 1,3-butadiene and a cyclohexane solution of styrene were added to yield 67.5 g of 1,3-butadiene and 7.5 g of styrene. Then, 0.6 mmol of 2,2-ditetrahydrofurylpropane was added, and 0.8 mmol of n-butyllithium was added. Subsequently, the mixture was polymerized for 1.5 hours at 50° C. Next, 0.72 mmol of N,N-bis(trimethylsilyl)-3-[diethoxy(methyl)silyl] propylamine was added as a modifying agent to the polymerization reaction system when the polymerization conversion ratio reached nearly 100%, and a denaturation reaction was carried out for 30 minutes at 50° C. Subsequently, the reaction was stopped by adding 2 mL of an isopropanol solution containing 5 mass % of 2,6-di-t-butyl-p-cresol (BHT), and the result was dried with an ordinary method to obtain the modified styrene-butadiene rubber 1 (modified SBR 1). Measurement of the microstructure of the resulting modified SBR 1 revealed a bound styrene content of 10 mass %, a vinyl bond content of the butadiene portion of 40%, and a peak molecular weight of 200,000.
<Modified Styrene-Butadiene Rubber 2>
Apart from using N-(1,3-dimethylbutylidene)-3-triethoxysilyl-1-propanamine instead of the N,N-bis(trimethylsilyl)-3-[diethoxy(methyl)silyl] propylamine as the modifying agent, a polymerization reaction and denaturation reaction were carried out in the same way as for the modified SBR 1 to obtain the modified styrene-butadiene rubber 2 (modified SBR 2). Measurement of the microstructure of the resulting modified SBR 2 revealed a bound styrene content of 10 mass %, a vinyl bond content of the butadiene portion of 40%, and a peak molecular weight of 200,000.
<Production and Evaluation of Tires>
The rubber compositions obtained as described above were used in treads to produce pneumatic radial tires for passenger vehicles with a size of 195/65R15. The rolling resistance and the steering stability on dry and wet road surfaces were evaluated for the tires using the methods below.
In Table 2 and Table 3, the edge component ratio derived from the lug grooves is the sum of the tire widthwise extending length of the lug grooves on the tread surface divided by the tire circumferential length, and the edge component ratio derived from the widthwise sipes is the sum of the tire widthwise extending length of the widthwise sipes on the tread surface divided by the tire circumferential length. These values are listed for each of the entire tread, the tread center portion, and the tread shoulder portions.
The tire tread pattern of Example 1 and Comparative Example 2 in Table 2 and the Examples and Comparative Examples in Table 3 was as illustrated in
On the other hand, the tire tread pattern of Comparative Example 1 and Comparative Example 3 in Table 2 was as illustrated in
The tire tread pattern of the tire of Examples 2 and 3 and Comparative Example 4 in Table 2 was similar to that of
(3) Rolling Resistance
Sample tires were rotated at a speed of 80 km/hr in a rotating drum under a load of 4.82 kN, and the rolling resistance was measured. The results are listed as index values, with the rolling resistance of the tire of Comparative Example 1 as 100. A smaller index value represents lower rolling resistance.
(4) Steering Stability on Dry and Wet Road Surfaces
The sample tires were mounted on a test car, and the steering stability on dry and wet road surfaces was represented as a feeling score by the driver. The results are listed as index values, with the feeling score of the tire of Comparative Example 1 as 100. A larger index value represents better steering stability.
As is clear from Table 2 and Table 3, the pneumatic tires of the Examples of the present disclosure can greatly improve the steering stability on dry and wet road surfaces without worsening of the rolling resistance.
The present disclosure can provide a pneumatic tire that can greatly improve the steering stability on dry and wet road surfaces without worsening of the rolling resistance. This tire can be used on various types of vehicles.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-106141 | May 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2017/019799 | 5/26/2017 | WO | 00 |
