JP7762052B2 - Rubber composition and tire - Google Patents

Description

The present invention relates to a rubber composition and a tire using the same.

Rubber compositions used in tires, anti-vibration rubber, conveyor belts, etc. generally contain diene rubber as the rubber component, and are compounded with vulcanizing agents such as sulfur, vulcanization accelerators, and metal oxides such as zinc oxide. Vulcanized rubber is formed by vulcanizing this rubber composition. In this vulcanization mechanism, metal oxides such as zinc oxide act as vulcanization accelerators and are used as essential components.

However, in recent years, there has been a demand to reduce the amount of metal oxides such as zinc oxide added to prevent environmental pollution. Therefore, for example, Patent Document 1 discloses a rubber composition in which 50% by mass or more of the rubber component is solution-polymerized styrene-butadiene rubber. Patent Document 2 discloses a rubber composition in which 50% by mass or more of the rubber component is solution-polymerized styrene-butadiene rubber with modified molecular ends. Furthermore, Patent Document 3 discloses the addition of a thiazole derivative having two or more thiol groups to a diene rubber together with a vulcanizing agent, with the aim of suppressing reversion even when the zinc atom concentration in the rubber composition is low.

Japanese Patent Application Laid-Open No. 2019-099709 Japanese Patent Application Laid-Open No. 2019-099708 JP 2017-088789 A

Metal oxides such as zinc oxide, which are used as essential materials for vulcanization accelerators, are useful for suppressing reversion when rubber compositions are vulcanized at high temperatures. Therefore, reducing the zinc oxide content or eliminating zinc oxide altogether can lead to the problem of reversion occurring more easily.

In view of the above, an embodiment of the present invention aims to provide a rubber composition that can suppress reversion while reducing or eliminating the amount of metal oxides such as zinc oxide.

A rubber composition according to an embodiment of the present invention comprises a diene rubber, a filler, and a silane coupling agent, wherein the diene rubber contains 40% by mass or more of natural rubber, and the filler content is 30 to 200 parts by mass, the silane coupling agent content is 5 parts by mass or more, and the metal oxide content is less than 0.5 parts by mass, per 100 parts by mass of the diene rubber. Here, a metal oxide content of less than 0.5 parts by mass also includes a case where the metal oxide content is 0 parts by mass, i.e., no metal oxide is present.

The tire according to the embodiment of the present invention is made using the above rubber composition.

According to an embodiment of the present invention, reversion can be suppressed while reducing or eliminating the amount of metal oxides such as zinc oxide.

The rubber composition according to this embodiment contains a diene rubber containing 40% or more by mass of natural rubber, a filler, and a silane coupling agent, and the metal oxide content is less than 0.5 parts by mass per 100 parts by mass of diene rubber. Metal oxides such as zinc oxide act as vulcanization accelerators, and reducing the amount of metal oxide or not incorporating it at all can easily cause reversion, in which bonds formed by vulcanization are broken. In contrast, by incorporating a silane coupling agent into a rubber composition in which the amount of natural rubber in the diene rubber is 40% or more by mass, the reversion suppression effect can be enhanced, and a reversion suppression effect equal to or greater than that achieved when metal oxide is incorporated in the usual amount can be achieved.

In the rubber composition according to this embodiment, the diene rubber serving as the rubber component contains 40% by mass or more of natural rubber (NR), i.e., 40 parts by mass or more of natural rubber per 100 parts by mass of diene rubber. The amount of natural rubber relative to the total mass of the diene rubber may be 50% by mass or more, 60% by mass or more, 70% by mass or more, or even 100% by mass.

Diene rubber refers to rubber with repeating units corresponding to diene monomers with conjugated double bonds, and has double bonds in the polymer backbone. Diene rubber may be natural rubber alone, or natural rubber may be used in combination with other diene rubbers. Other diene rubbers are not particularly limited, and include, for example, isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, and styrene-isoprene-butadiene copolymer rubber, among other diene rubbers commonly used in rubber compositions. These may be used alone or in combination of two or more. Among these, it is preferable to use at least one of butadiene rubber or styrene-butadiene rubber as the other diene rubber. The diene rubbers mentioned above also include those whose terminals have been modified as needed (e.g., terminally modified SBR) and those whose properties have been modified to impart desired characteristics (e.g., modified NR).

In one embodiment, 100% by mass of diene-based rubber may include 40 to 80% by mass (more preferably 50 to 70% by mass) of natural rubber and 20 to 60% by mass (more preferably 30 to 50% by mass) of styrene-butadiene rubber and/or butadiene rubber. In another embodiment, 100% by mass of diene-based rubber may include 40 to 80% by mass (more preferably 50 to 70% by mass) of natural rubber, 10 to 55% by mass (more preferably 15 to 30% by mass) of styrene-butadiene rubber, and 5 to 50% by mass (more preferably 10 to 20% by mass) of butadiene rubber.

It is preferable to use carbon black and/or silica as the filler to be compounded into the rubber composition.

There are no particular limitations on the carbon black, and various known varieties can be used. Specific examples include SAF grade (N100 series), ISAF grade (N200 series), HAF grade (N300 series), FEF grade (N500 series), and GPF grade (N600 series) (all ASTM grades). These grades of carbon black can be used alone or in combination of two or more.

The silica is not particularly limited, and examples include wet silica and dry silica. It is preferable to use wet silica such as wet precipitation silica or wet gelation silica.

The filler content is preferably 30 to 200 parts by mass per 100 parts by mass of diene rubber, and can be set appropriately depending on the application, etc. The filler content per 100 parts by mass of diene rubber is preferably 40 to 150 parts by mass, more preferably 45 to 120 parts by mass, and may be 50 to 100 parts by mass. The carbon black content may be 5 to 150 parts by mass, 10 to 120 parts by mass, 20 to 100 parts by mass, or 30 to 80 parts by mass per 100 parts by mass of diene rubber. The silica content may be 10 to 150 parts by mass, 20 to 120 parts by mass, or 30 to 100 parts by mass per 100 parts by mass of diene rubber.

In one embodiment, the filler may be primarily composed of carbon black. That is, the amount of carbon black relative to the total mass of the filler may be greater than 50 mass%, greater than 70 mass%, or even 100 mass%. In this case, for example, the amount of carbon black may be 30 to 120 mass parts and silica 0 to 30 mass parts, or 40 to 100 mass parts and silica 0 to 20 mass parts per 100 mass parts of diene rubber.

In one embodiment, the filler may be primarily composed of silica. That is, the amount of silica relative to the total mass of the filler may be greater than 50 mass%, greater than 60 mass%, greater than 70 mass%, or even 100 mass%. In this case, for example, the amount of silica may be 30 to 120 mass parts and carbon black 5 to 50 mass parts, or 40 to 100 mass parts and carbon black 5 to 20 mass parts per 100 mass parts of diene rubber.

A silane coupling agent is compounded into the rubber composition according to this embodiment. As described above, reducing the amount of metal oxide or not compounding it at all can easily cause reversion, but compounding a silane coupling agent can suppress reversion, and this effect can be further enhanced, particularly in rubber compositions that contain a large amount of natural rubber.

Examples of silane coupling agents include sulfide silane coupling agents such as bis(3-triethoxysilylpropyl)tetrasulfide, bis(3-triethoxysilylpropyl)disulfide, bis(2-triethoxysilylethyl)tetrasulfide, bis(4-triethoxysilylbutyl)disulfide, bis(3-trimethoxysilylpropyl)tetrasulfide, and bis(2-trimethoxysilylethyl)disulfide; 3-mercaptopropyltrimethoxysilane; Examples of suitable silane coupling agents include mercaptosilane coupling agents such as mercaptotriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyldimethylmethoxysilane, and mercaptoethyltriethoxysilane; and thioester group-containing silane coupling agents such as 3-octanoylthio-1-propyltriethoxysilane, 3-propionylthiopropyltrimethoxysilane, 3-hexanoylthio-1-propyltriethoxysilane, and 3-octanoylthio-1-propyltrimethoxysilane. These can be used alone or in combination of two or more. Of these, it is preferable to use a sulfide silane coupling agent as the silane coupling agent, as this can further enhance the reversion suppression effect.

The amount of silane coupling agent is 5 parts by mass or more per 100 parts by mass of diene rubber. By incorporating 5 parts by mass or more in this manner, the effect of suppressing reversion can be enhanced, and a decrease in rubber strength due to reversion can be suppressed. The amount of silane coupling agent is more preferably 7 parts by mass or more per 100 parts by mass of diene rubber. From the perspective of suppressing reversion, there is no particular upper limit to the amount of silane coupling agent. However, from the perspective of suppressing a decrease in strength, the amount of silane coupling agent is preferably 40% by mass or less of the filler content, and may be 30% by mass or less. In one embodiment, the amount of silane coupling agent may be 5 to 20 parts by mass per 100 parts by mass of diene rubber.

Generally, silane coupling agents are used in combination with silica as a filler, but in this embodiment, a silane coupling agent is compounded even when silica is not used as a filler. Even when silica is used as a filler, the silane coupling agent is compounded in an amount of 5 parts by mass or more per 100 parts by mass of diene rubber, regardless of the silica content. In one embodiment, the silane coupling agent may be included in the rubber composition in an amount greater than 20 parts by mass per 100 parts by mass of silica.

In the rubber composition according to this embodiment, from the viewpoint of preventing environmental pollution, the metal oxide content is less than 0.5 parts by mass, more preferably less than 0.2 parts by mass, and even more preferably 0 parts by mass, i.e., no metal oxide, per 100 parts by mass of diene rubber. Here, when multiple types of metal oxides are contained, the metal oxide content refers to the total amount.

Metal oxides are oxides of metal elements, but do not include oxides containing metalloid elements. Here, metal elements are elements (excluding hydrogen) located to the left of the line connecting boron, silicon, germanium, antimony, and bismuth (these are metalloid elements) in the periodic table. A typical example of a metal oxide is zinc oxide, but other examples include magnesium oxide and calcium oxide.

In addition to the above components, the rubber composition according to this embodiment may contain various additives commonly used in rubber compositions, such as oil, stearic acid, antioxidants, waxes, vulcanizing agents, and vulcanization accelerators.

Examples of antioxidants include aromatic amine-based antioxidants, amine-ketone-based antioxidants, monophenol-based antioxidants, bisphenol-based antioxidants, polyphenol-based antioxidants, dithiocarbamate-based antioxidants, and thiourea-based antioxidants. These can be used alone or in combination of two or more. The amount of antioxidant is not particularly limited, and may be, for example, 0.5 to 10 parts by mass per 100 parts by mass of diene rubber.

Sulfur is preferably used as the vulcanizing agent, and examples include powdered sulfur, precipitated sulfur, insoluble sulfur, and highly dispersible sulfur. The content of the vulcanizing agent is not particularly limited, and may be, for example, 0.1 to 10 parts by mass or 0.5 to 5 parts by mass per 100 parts by mass of diene rubber.

Vulcanization accelerators include, for example, sulfenamide-based, thiuram-based, thiazole-based, and guanidine-based vulcanization accelerators, and any of these can be used alone or in combination of two or more. The amount of vulcanization accelerator added is not particularly limited, and may be, for example, 0.1 to 10 parts by mass or 0.5 to 5 parts by mass per 100 parts by mass of diene rubber.

The rubber composition according to this embodiment can be prepared by kneading in accordance with conventional methods using a commonly used mixer such as a Banbury mixer, kneader, or roll. For example, in the first mixing stage (non-pro kneading process), additives other than the vulcanizing agent and vulcanization accelerator, along with the filler and silane coupling agent, are added to and mixed with the diene rubber. Then, in the final mixing stage (pro kneading process), the vulcanizing agent and vulcanization accelerator are added to and mixed with the resulting mixture to prepare an unvulcanized rubber composition.

The rubber composition according to this embodiment can be used for various rubber components such as tires, anti-vibration rubber, and conveyor belts. It is preferably used for tires, and can be applied to various tire components such as the tread, sidewall, and bead portions of pneumatic tires of various sizes for various uses such as passenger car tires and large truck and bus tires.

In one embodiment, a tire including a rubber portion (e.g., tread rubber, sidewall rubber, etc.) made from the above-described rubber composition is manufactured as follows. The rubber composition is molded into a desired shape using a conventional method, for example, extrusion processing. The resulting molded product is combined with other components to produce a green tire. The green tire can then be vulcanized and molded at, for example, 140 to 180°C to produce a pneumatic tire.

The following examples are provided, but the present invention is not limited to these examples.

The components used in the examples and comparative examples are as follows.
NR: Natural rubber "RSS#3"
・BR: Butadiene rubber, "BR150B" manufactured by Ube Industries, Ltd.
SBR: Styrene butadiene rubber (terminally modified), "HPR840" manufactured by JSR Corporation
Carbon black: "Seast 3" manufactured by Tokai Carbon Co., Ltd.
Silica: "Ultrasil VN3" manufactured by Evonik Industries
Silane coupling agent 1: bis(3-triethoxysilylpropyl)tetrasulfide, "Si69" manufactured by Evonik
Silane coupling agent 2: bis(3-triethoxysilylpropyl) disulfide, "Si75" manufactured by Evonik
Silane coupling agent 3: 3-octanoylthio-1-propyltriethoxysilane, "NXT" manufactured by Momentive
Oil: JXTG Nippon Oil & Energy Corporation "Process NC-140"
Zinc oxide: "Zinc oxide type 2" manufactured by Mitsui Mining & Smelting Co., Ltd.
Stearic acid: "Lunac S-20" manufactured by Kao Corporation
Anti-aging agent: "Antigen 6C" manufactured by Sumitomo Chemical Co., Ltd.
Sulfur: "5% oil-filled powder sulfur" manufactured by Tsurumi Chemical Industry Co., Ltd.
Vulcanization accelerator CBS: "Noccela CZ-G (CZ)" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Vulcanization accelerator DPG: "Noccela D" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.

The evaluation methods used in the examples and comparative examples are as follows.
(1) Reversion Suppression Index For unvulcanized rubber compositions, the rheometer curve (torque) was measured at 175°C in accordance with the conditions of JIS K6300-2:2013, and the reversion properties were determined using the following formula, and the reciprocal thereof was calculated. The reciprocal of the reversion properties of Comparative Example 1 in Table 1, Comparative Example 4 in Table 2, Comparative Example 7 in Table 3, and Comparative Example 10 in Table 4 was set to 100, and the reversion suppression index of each Example and Comparative Example was determined. A larger index indicates a more excellent reversion suppression effect.
Reversion (%) = [(MH-M15)/(MH-ML)] x 100
In the formula, MH represents the maximum torque value, ML represents the minimum torque value, and M15 represents the torque value 15 minutes after the start of measurement.

(2) Tensile strength (M100)
Rubber samples were prepared by vulcanizing unvulcanized rubber compositions by heating at 175°C for 15 minutes. Samples were prepared using JIS No. 3 dumbbells and the 100% modulus M100 (MPa) was measured in accordance with JIS K6251. The tensile strength of each Example and Comparative Example was expressed as an index, with the M100 of Comparative Example 1 in Table 1, the M100 of Comparative Example 4 in Table 2, the M100 of Comparative Example 7 in Table 3, and the M100 of Comparative Example 10 in Table 4 all being set to 100. The smaller the index, the greater the decrease in rubber strength due to reversion.

[Examples 1 to 4 and Comparative Examples 1 to 3]
Using a Banbury mixer, in the first mixing stage, compounding ingredients except for sulfur and vulcanization accelerator were added to natural rubber and kneaded (discharge temperature = 150°C) according to the formulation (parts by mass) shown in Table 1 below. Next, in the final mixing stage, sulfur and vulcanization accelerator were added to the resulting kneaded mixture and kneaded (discharge temperature = 90°C). Each rubber composition thus obtained was evaluated for reversion inhibition index and tensile strength (M100). The results are shown in Table 1.

The examples shown in Table 1 use NR as the diene rubber alone and carbon black as the filler alone. In this case, Comparative Example 2, which simply excluded zinc oxide, experienced greater reversion and a greater decrease in tensile strength than Comparative Example 1, which contained zinc oxide. In contrast, Examples 1 to 4, which contained a silane coupling agent, suppressed reversion to the same level as Comparative Example 1, which did contain zinc oxide, and also significantly improved the decrease in tensile strength seen in Comparative Example 2.

[Examples 5 to 9 and Comparative Examples 4 to 6]
Rubber compositions were prepared in the same manner as in Example 1, with the formulation (parts by mass) shown in Table 2 below. The reversion inhibition index and tensile strength (M100) of each obtained rubber composition were evaluated. The results are shown in Table 2.

The example shown in Table 2 uses a diene rubber with a NR/BR ratio of 50/50 and a combination of carbon black and silica as the filler. In this case, as in the case of Table 1, Examples 5 to 9, which contain a silane coupling agent, suppressed reversion to the same level as Comparative Example 4, which contains zinc oxide, despite not containing zinc oxide, and also significantly improved the decrease in tensile strength seen in Comparative Example 5. Furthermore, when comparing the types of silane coupling agents at the same compounding amounts, those using sulfide silane coupling agents tended to have greater effects in suppressing reversion and improving tensile strength.

[Examples 10 to 13 and Comparative Examples 7 to 9]
Rubber compositions were prepared in the same manner as in Example 1, with the formulation (parts by mass) shown in Table 3 below. The reversion inhibition index and tensile strength (M100) of each obtained rubber composition were evaluated. The results are shown in Table 3.

The examples shown in Table 3 use a diene rubber with a NR/BR/SBR ratio of 60/20/20 and a combination of carbon black and silica as the filler. In this case, as in the case of Table 1, Examples 10 to 13, which contain a silane coupling agent, suppressed reversion to the same level as Comparative Example 7, which contains zinc oxide, despite not containing zinc oxide, and also significantly improved the decrease in tensile strength seen in Comparative Example 8.

[Examples 14 to 18 and Comparative Examples 10 to 12]
Rubber compositions were prepared in the same manner as in Example 1, with the formulation (parts by mass) shown in Table 4 below. The reversion inhibition index and tensile strength (M100) of each obtained rubber composition were evaluated. The results are shown in Table 4.

The examples shown in Table 4 use a diene rubber with a NR/BR/SBR ratio of 40/10/50 and a combination of carbon black and silica as the filler. In this case, as in the case of Table 1, Examples 14 to 18, which contain a silane coupling agent, suppressed reversion to the same level as Comparative Example 10, which contains zinc oxide, despite not containing zinc oxide, and also significantly improved the decrease in tensile strength seen in Comparative Example 11.

The various numerical ranges described in this specification can each be combined with any upper and lower limit, and all such combinations are considered to be preferred numerical ranges and are described in this specification. Furthermore, a numerical range described as "X to Y" means greater than or equal to X and less than or equal to Y.

Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be embodied in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included within the scope and spirit of the invention, as well as within the scope of the inventions and their equivalents as set forth in the claims.

Claims (4)

The composition includes a diene rubber, a filler, and a silane coupling agent,
The diene rubber contains 40% by mass or more of natural rubber,
the content of the filler is 30 to 200 parts by mass, the content of the silane coupling agent is 5 parts by mass or more, and the content of the metal oxide is less than 0.5 parts by mass , relative to 100 parts by mass of the diene rubber;
The rubber composition , wherein the filler contains carbon black, and the amount of carbon black relative to the total mass of the filler is 100% by mass . The rubber composition according to claim 1, wherein the silane coupling agent includes a sulfide silane coupling agent. The rubber composition according to claim 1 or 2, wherein the content of the silane coupling agent is 40 mass% or less relative to the content of the filler. A tire made using the rubber composition described in any one of claims 1 to 3.