Rubber composition, and rubber crosslinked product and pneumatic tire using said rubber composition

Abstract

Provided is a rubber composition that contains a diene-based rubber and a hydrocarbon resin. The contained amount of the hydrocarbon resin is 1-200 parts by mass with respect to 100 parts by mass of the diene-based rubber. The hydrocarbon resin includes: aliphatic monomer units; or aliphatic monomer units and aromatic monomer units. The rubber composition has a number average molecular weight (Mn) in the range of 400-3000, a weight average molecular weight (Mw) in the range of 700-6000, a Z-average molecular weight (Mz) in the range of 1500-20000, a ratio (Mw / Mn) of the weight average molecular weight with respect to the number average molecular weight in the range of 1.0-4.0, a ratio (Mz / Mw) of the Z-average molecular weight with respect to the weight average molecular weight in the range of 1.0-3.5, a ratio (Mp / Mw) of a peak-top molecular weight (Mp) with respect to the weight average molecular weight (Mw) in the range of 0.4-0.8, and a softening temperature in the range of 80-150°C.

Description

Rubber composition, cross-linked rubber product using the same, and pneumatic tire

[0001] The present invention relates to a rubber composition, and more particularly to a rubber composition that can give a cross-linked rubber product that has an excellent balance of rolling resistance, wet grip performance, and low-temperature performance.

[0002] In recent years, automobile tires have been strongly required to have low fuel consumption due to environmental and resource issues, while, for example, improved wet grip performance is also required from the viewpoint of safety. A cross-linked product of a rubber composition in which silica is blended as a filler in the rubber component has lower rolling resistance when used in a tire than a cross-linked product of a rubber composition in which carbon black is blended. Therefore, by using a cross-linked product of a rubber composition in which silica is blended to form a tire, a tire with excellent fuel economy can be obtained.

[0003] However, even when silica is compounded into a conventional rubber component, the affinity between the rubber component and silica is insufficient, and they tend to separate. As a result, the cross-linked rubber obtained by cross-linking them has problems such as insufficient rolling resistance and low-temperature performance when used to form a tire.

[0004] For example, Patent Document 1 discloses that, for the purpose of improving the rolling resistance and wet grip performance of a tire, a specific amount of a softener having a specific structure is blended into a rubber component, and a specific amount of a hydrocarbon resin having a specific structure is blended into the rubber component.

[0005] JP 2010-241965 A

[0006] According to the softener and hydrocarbon resin having a specific structure described in Patent Document 1, when a tire is manufactured using a rubber composition obtained by adding these, it is possible to improve both rolling resistance and wet grip performance to a certain extent. However, from the viewpoint of further improving fuel economy and safety, further improvements in rolling resistance and wet grip performance are required, and in addition, excellent low-temperature performance is also required.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a rubber composition that can give a cross-linked rubber product that has an excellent balance of rolling resistance, wet grip performance, and low-temperature performance.

[0008] The present inventors have conducted studies to achieve the above object, and have found that the above object can be achieved by a rubber composition obtained by blending a specific hydrocarbon resin with a diene rubber, specifically, a rubber composition obtained by blending a hydrocarbon resin whose number average molecular weight (Mn), weight average molecular weight (Mw), Z average molecular weight (Mz), ratio of weight average molecular weight to number average molecular weight (Mw / Mn), ratio of Z average molecular weight to weight average molecular weight (Mz / Mw), and softening point are all within specific ranges, and whose ratio of peak top molecular weight (Mp) to weight average molecular weight (Mw) (Mp / Mw) is controlled in the range of 0.4 to 0.8, thereby completing the present invention.

[0009] That is, according to the present invention, there is provided a rubber composition containing a diene rubber and a hydrocarbon resin, wherein the content of the hydrocarbon resin is 1 to 200 parts by mass per 100 parts by mass of the diene rubber, and the hydrocarbon resin contains aliphatic monomer units, or aliphatic monomer units and aromatic monomer units, and has a number average molecular weight (Mn) in the range of 400 to 3000, a weight average molecular weight (Mw) in the range of 700 to 6000, a Z average molecular weight (Mz) in the range of 1500 to 20000, a ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) in the range of 1.0 to 4.0, a ratio of the Z average molecular weight to the weight average molecular weight (Mz / Mw) in the range of 1.0 to 3.5, a ratio of the peak top molecular weight (Mp) to the weight average molecular weight (Mw) in the range of 0.4 to 0.8, and a softening point temperature in the range of 80 to 150°C. A rubber composition is provided.

[0010] In the rubber composition of the present invention, the hydrocarbon resin preferably contains 1 to 70 mass% of 1,3-pentadiene monomer units, 1 to 30 mass% of alicyclic monoolefin monomer units having 4 to 6 carbon atoms, 0 to 15 mass% of isoprene monomer units, 0 to 50 mass% of acyclic monoolefin monomer units having 4 to 8 carbon atoms, 0 to 10 mass% of alicyclic diolefin monomer units, and 0 to 40 mass% of aromatic monoolefin monomer units.

[0011] In the rubber composition of the present invention, the hydrocarbon resin is preferably a hydride. The rubber composition of the present invention preferably further contains a filler. The rubber composition of the present invention preferably further contains a cross-linking agent. The rubber composition of the present invention preferably contains a styrene-butadiene copolymer rubber or a butadiene rubber as the diene rubber.

[0012] According to the present invention, there is also provided a cross-linked rubber product obtained by cross-linking the above rubber composition. Furthermore, according to the present invention, there is provided a pneumatic tire characterized in that the above rubber composition or the above cross-linked rubber product is used in the tread.

[0013] According to the present invention, it is possible to provide a rubber composition that can give a cross-linked rubber product that has an excellent balance of rolling resistance, wet grip performance, and low-temperature performance.

[0014] The rubber composition of the present invention is a rubber composition containing a diene rubber and a hydrocarbon resin, wherein the content of the hydrocarbon resin is 1 to 200 parts by mass per 100 parts by mass of the diene rubber. Each component of the rubber composition of the present invention will be described below.

[0015] <Hydrocarbon Resin> The hydrocarbon resin used in the present invention contains aliphatic monomer units, or aliphatic monomer units and aromatic monomer units, and has a number average molecular weight (Mn) in the range of 400 to 3000, a weight average molecular weight (Mw) in the range of 700 to 6000, a Z average molecular weight (Mz) in the range of 1500 to 20000, a ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) in the range of 1.0 to 4.0, a ratio of the Z average molecular weight to the weight average molecular weight (Mz / Mw) in the range of 1.0 to 3.5, a ratio of the peak top molecular weight (Mp) to the weight average molecular weight (Mw) in the range of 0.4 to 0.8, and a softening point temperature in the range of 80 to 150°C.

[0016] The hydrocarbon resin used in the present invention may be any resin containing at least an aliphatic monomer unit, and may also contain an aromatic monomer unit in addition to the aliphatic monomer unit.

[0017] (Aliphatic Monomer Units) First, the aliphatic monomer units contained in the hydrocarbon resin used in the present invention will be described. The aliphatic monomer for forming the aliphatic monomer units may be any monomer that does not contain an aromatic ring and contains at least an unsaturated hydrocarbon. Examples of such aliphatic monomers include 1,3-pentadiene, alicyclic monoolefin monomers having 4 to 6 carbon atoms, isoprene, acyclic monoolefin monomers having 4 to 8 carbon atoms, and alicyclic diolefin monomers. Furthermore, in the present invention, a mixture containing these aliphatic monomers may be added to the polymerization reaction system when producing the hydrocarbon resin. In this case, the aliphatic monomers contained in the mixture are used as components of the monomer units that constitute the hydrocarbon resin. It is also possible to use addition-polymerizable components other than the aliphatic monomers contained in the mixture as components of the monomer units of the hydrocarbon resin, and non-addition-polymerizable components as solvents during polymerization. As a mixture containing such aliphatic monomers, for example, a C5 fraction containing aliphatic monomers such as 1,3-pentadiene, cyclopentene, and isobutylene can be suitably used.

[0018] The hydrocarbon resin preferably contains, as aliphatic monomer units, 1,3-pentadiene monomer units and alicyclic monoolefin monomer units having 4 to 6 carbon atoms, and may further contain, in addition to these, isoprene monomer units, acyclic monoolefin monomer units having 4 to 8 carbon atoms, and alicyclic diolefin monomer units.

[0019] The content of 1,3-pentadiene monomer units in the hydrocarbon resin is not particularly limited, but is preferably 1 to 70 mass%, more preferably 20 to 65 mass%, even more preferably 30 to 60 mass%, and particularly preferably 35 to 52 mass%. By setting the content of 1,3-pentadiene monomer units within the above range, the obtained cross-linked rubber product can be made to have even better rolling resistance, wet grip performance, and low-temperature performance. The cis / trans isomer ratio in 1,3-pentadiene may be any ratio and is not particularly limited.

[0020] The alicyclic monoolefin having 4 to 6 carbon atoms that forms the alicyclic monoolefin monomer unit having 4 to 6 carbon atoms is a hydrocarbon compound having one ethylenically unsaturated bond and a non-aromatic ring structure in its molecular structure. Specific examples of the alicyclic monoolefin having 4 to 6 carbon atoms include cyclobutene, cyclopentene, cyclohexene, methylcyclobutene, and methylcyclopentene.

[0021] The content of the alicyclic monoolefin monomer unit having 4 to 6 carbon atoms in the hydrocarbon resin is not particularly limited, but is preferably 1 to 30 mass%, more preferably 5 to 25 mass%, even more preferably 9 to 22 mass%, still more preferably 11 to 19 mass%, and particularly preferably 13 to 17 mass%. By setting the content of the alicyclic monoolefin monomer unit having 4 to 6 carbon atoms within the above range, the obtained cross-linked rubber product can be made to have even better rolling resistance, wet grip performance, and low-temperature performance.

[0022] The proportion of each compound corresponding to the alicyclic monoolefin having 4 to 6 carbon atoms may be any proportion and is not particularly limited, but it is preferable that at least cyclopentene is contained, and the proportion of cyclopentene in the alicyclic monoolefin having 4 to 6 carbon atoms is more preferably 50 mass% or more, further preferably 80 mass% or more, and particularly preferably 100 mass%.

[0023] Furthermore, the hydrocarbon resin used in the present invention preferably contains an isoprene monomer unit, and by containing the isoprene monomer unit, the wet grip performance of the obtained cross-linked rubber product can be further improved. The content of the isoprene monomer unit in the hydrocarbon resin is not particularly limited, but is preferably 0 to 15 mass%, more preferably 0.1 to 12 mass%, even more preferably 0.15 to 10 mass%, and even more preferably 0.2 to 9 mass%. By setting the content of the isoprene monomer unit within the above range, the wet grip performance of the obtained cross-linked rubber product can be more appropriately improved. Note that, from the viewpoint of further improving the wet grip performance of the obtained cross-linked rubber product, the content of the isoprene monomer unit is particularly preferably 6 to 10 mass%, and from the viewpoint of obtaining an obtained cross-linked rubber product with an even better balance of rolling resistance, wet grip performance, and low-temperature performance, the content of the isoprene monomer unit is particularly preferably 0.15 to 0.5 mass%.

[0024] The acyclic monoolefin having 4 to 8 carbon atoms forming the acyclic monoolefin monomer unit having 4 to 8 carbon atoms is a chain hydrocarbon compound having 4 to 8 carbon atoms and no ring structure, and having one ethylenically unsaturated bond in its molecular structure. Specific examples of the acyclic monoolefin having 4 to 8 carbon atoms include butenes such as 1-butene, 2-butene, and isobutylene (2-methylpropene); pentenes such as 1-pentene, 2-pentene, 2-methyl-1-butene, 3-methyl-1-butene, and 2-methyl-2-butene; hexenes such as 1-hexene, 2-hexene, and 2-methyl-1-pentene; heptenes such as 1-heptene, 2-heptene, and 2-methyl-1-hexene; and octenes such as 1-octene, 2-octene, 2-methyl-1-heptene, and diisobutylene (2,4,4-trimethyl-1-pentene and 2,4,4-trimethyl-1-pentene).

[0025] The content of the acyclic monoolefin monomer unit having 4 to 8 carbon atoms in the hydrocarbon resin is not particularly limited, but is preferably 0 to 50 mass%, more preferably 8 to 45 mass%, even more preferably 10 to 40 mass%, and particularly preferably 14 to 37 mass%. By setting the content of the acyclic monoolefin monomer unit having 4 to 8 carbon atoms within the above range, the obtained cross-linked rubber product can be made to have even better rolling resistance, wet grip performance, and low-temperature performance.

[0026] The proportion of each corresponding compound (including isomers) in the acyclic monoolefin having 4 to 8 carbon atoms may be any proportion and is not particularly limited, but it is preferable that at least one selected from the group consisting of 2-methyl-2-butene, isobutylene, and diisobutylene is included, and it is more preferable that the total amount of 2-methyl-2-butene, isobutylene, and diisobutylene accounts for 50 mass% or more of the acyclic monoolefin having 4 to 8 carbon atoms.

[0027] The alicyclic diolefin forming the alicyclic diolefin monomer unit is a hydrocarbon compound having two or more ethylenically unsaturated bonds and a non-aromatic ring structure in its molecular structure. Specific examples of the alicyclic diolefin include cyclopentadiene, cyclopentadiene polymers such as dicyclopentadiene, methylcyclopentadiene, and methylcyclopentadiene polymers.

[0028] The content of the alicyclic diolefin monomer unit in the hydrocarbon resin is not particularly limited, but is preferably 0 to 10 mass%, more preferably 0.03 to 5 mass%, even more preferably 0.05 to 4 mass%, and particularly preferably 0.08 to 3 mass%. By setting the content of the alicyclic diolefin monomer unit within the above range, the obtained cross-linked rubber product can be made to have even better rolling resistance, wet grip performance, and low-temperature performance.

[0029] The hydrocarbon resin of the present invention may also contain other monomer units in addition to the 1,3-pentadiene monomer unit, the alicyclic monoolefin monomer unit having 4 to 6 carbon atoms, the isoprene monomer unit, the acyclic monoolefin monomer unit having 4 to 8 carbon atoms, and the alicyclic diolefin monomer unit.

[0030] The other monomers forming such other monomer units are not particularly limited as long as they are addition-polymerizable compounds that can be addition-copolymerized with 1,3-pentadiene, etc. Examples of such other monomers include unsaturated hydrocarbons having 4 to 6 carbon atoms other than 1,3-pentadiene and isoprene, such as 1,3-butadiene, 1,2-butadiene, 1,3-hexadiene, and 1,4-pentadiene; alicyclic monoolefins having 7 or more carbon atoms, such as cycloheptene; and acyclic monoolefins having 4 to 8 carbon atoms other than ethylene, propylene, and nonene.

[0031] The content of other monomer units in the hydrocarbon resin is usually in the range of 0 to 30% by mass, preferably 0 to 25% by mass, and more preferably 0 to 20% by mass.

[0032] The content of aliphatic monomer units in the hydrocarbon resin is not particularly limited, but is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more. In particular, when the hydrocarbon resin contains aliphatic monomer units and aromatic monomer units, the content of the aliphatic monomer units is not particularly limited, but is preferably 60% by mass or more, more preferably 63 to 90% by mass, even more preferably 65 to 85% by mass, and particularly preferably 68 to 81% by mass.

[0033] (Aromatic Monomer Units) The hydrocarbon resin used in the present invention may contain aromatic monomer units in addition to aliphatic monomer units. By using a hydrocarbon resin containing aromatic monomer units in addition to aliphatic monomer units, the resulting cross-linked rubber product can have superior rolling resistance and wet grip performance. The aromatic monomer for forming the aromatic monomer units may be any monomer having an aromatic ring and capable of copolymerizing with an aliphatic monomer, such as an aromatic monoolefin monomer. In addition, in the present invention, a mixture containing an aromatic monomer such as an aromatic monoolefin monomer may be added to the polymerization reaction system when producing the hydrocarbon resin. In this case, the aromatic monomer contained in the mixture is used as a component of the monomer units constituting the hydrocarbon resin. It is also possible to use addition-polymerizable components other than the aromatic monomer contained in the mixture as components of the monomer units of the hydrocarbon resin, and the non-addition-polymerizable components as a solvent during polymerization. As a mixture containing such aromatic monomers, for example, a C9 fraction containing aromatic monomers such as styrene compounds and indene compounds can be suitably used.

[0034] The aromatic monoolefin monomer is an aromatic compound having one ethylenically unsaturated bond in its molecular structure. Specific examples of the aromatic monoolefin include styrene compounds such as styrene, α-methylstyrene, β-methylstyrene, and vinyltoluene; indene compounds such as indene and 1-methylindene; and coumarone.

[0035] The content of aromatic monoolefin monomer units in the hydrocarbon resin is not particularly limited, but is preferably 0 to 40 mass%, more preferably 10 to 37 mass%, even more preferably 15 to 35 mass%, and particularly preferably 19 to 32 mass%. By setting the content of aromatic monoolefin monomer units within the above range, the rolling resistance and wet grip performance of the obtained cross-linked rubber can be more appropriately improved.

[0036] The number average molecular weight (Mn) of the hydrocarbon resin used in the present invention is in the range of 400 to 3,000, preferably in the range of 500 to 2,000, more preferably in the range of 700 to 1,300, and even more preferably in the range of 800 to 1,100. The weight average molecular weight (Mw) of the hydrocarbon resin used in the present invention is in the range of 700 to 6,000, preferably in the range of 1,000 to 4,000, more preferably in the range of 1,400 to 3,000, and even more preferably in the range of 1,600 to 2,500. The Z average molecular weight (Mz) of the hydrocarbon resin used in the present invention is in the range of 1,500 to 20,000, preferably in the range of 2,200 to 10,000, more preferably in the range of 2,700 to 6,500, and even more preferably in the range of 3,200 to 5,700.

[0037] The ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) of the hydrocarbon resin used in the present invention is in the range of 1.0 to 4.0, preferably in the range of 1.2 to 3.2, more preferably in the range of 1.5 to 2.9, and even more preferably in the range of 1.7 to 2.6. The ratio of the Z average molecular weight to the weight average molecular weight (Mz / Mw) of the hydrocarbon resin used in the present invention is in the range of 1.0 to 3.5, preferably in the range of 1.2 to 3.2, more preferably in the range of 1.4 to 2.8, and even more preferably in the range of 1.6 to 2.5.

[0038] By setting the number average molecular weight (Mn), weight average molecular weight (Mw), Z average molecular weight (Mz), ratio of weight average molecular weight to number average molecular weight (Mw / Mn), and ratio of Z average molecular weight to weight average molecular weight (Mz / Mw) of the hydrocarbon resin within the above-mentioned ranges, the obtained cross-linked rubber product can be one that has an excellent balance of rolling resistance, wet grip performance, and low temperature performance.

[0039] The number average molecular weight (Mn), weight average molecular weight (Mw), Z average molecular weight (Mz), ratio of weight average molecular weight to number average molecular weight (Mw / Mn), and ratio of Z average molecular weight to weight average molecular weight (Mz / Mw) of the hydrocarbon resin can be determined as polystyrene-equivalent values ​​by gel permeation chromatography using tetrahydrofuran as a developing solvent.

[0040] In the present invention, the number average molecular weight (Mn), weight average molecular weight (Mw), Z average molecular weight (Mz), ratio of weight average molecular weight to number average molecular weight (Mw / Mn), and ratio of Z average molecular weight to weight average molecular weight (Mz / Mw) of the hydrocarbon resin are set within the above-mentioned ranges, and in addition, the ratio of peak top molecular weight (Mp) to weight average molecular weight (Mw) of the hydrocarbon resin (Mp / Mw) is set within the range of 0.4 to 0.8. In the present invention, a hydrocarbon resin having a ratio of peak top molecular weight (Mp) to weight average molecular weight (Mw) (Mp / Mw) within the range of 0.4 to 0.8 is used as the hydrocarbon resin, and by blending this with a diene rubber, the rubber composition thus obtained can provide a cross-linked rubber having an excellent balance of rolling resistance, wet grip performance, and low temperature performance. In particular, the present inventors have conducted extensive research and have found that by using a hydrocarbon resin in which the ratio (Mp / Mw) of peak top molecular weight (Mp) to weight average molecular weight (Mw) is in the range of 0.4 to 0.8, it is possible to obtain a tire that contains a relatively large amount of low molecular weight components, compared to when the ratio (Mp / Mw) is close to 1. This makes it possible to further improve wet grip performance and low temperature performance while maintaining good rolling resistance, and as a result, it is possible to obtain a tire that is excellent in balance among rolling resistance, wet grip performance, and low temperature performance.

[0041] If the ratio (Mp / Mw) of the peak top molecular weight (Mp) to the weight average molecular weight (Mw) is too low, rolling resistance will decrease. On the other hand, if the ratio (Mp / Mw) of the peak top molecular weight (Mp) to the weight average molecular weight (Mw) is too high, wet grip performance and low temperature performance will decrease. The ratio (Mp / Mw) of the peak top molecular weight (Mp) to the weight average molecular weight (Mw) may be in the range of 0.4 to 0.8, preferably in the range of 0.4 to 0.78, more preferably in the range of 0.41 to 0.75, even more preferably in the range of 0.43 to 0.72, particularly preferably in the range of 0.47 to 0.67, and most preferably in the range of 0.5 to 0.64. The peak top molecular weight (Mp) of the hydrocarbon resin is not particularly limited, but is preferably in the range of 500 to 4000, more preferably in the range of 700 to 2500, and even more preferably in the range of 1000 to 1500.

[0042] The ratio (Mp / Mw) of the peak top molecular weight (Mp) to the weight average molecular weight (Mw) is determined by measuring the weight average molecular weight (Mw) and peak top molecular weight (Mp) of a hydrocarbon resin as polystyrene equivalent values ​​using gel permeation chromatography (GPC) with tetrahydrofuran as a developing solvent, and then calculating the ratio (Mp / Mw). The peak top molecular weight (Mp) is the molecular weight at which the detected value (elution amount) is maximum in the GPC chart obtained by GPC measurement, and Mp / Mw represents the relationship between the peak top molecular weight (Mp), which is the molecular weight at which such detected value (elution amount) is maximum, and the weight average molecular weight (Mw). The smaller the Mp / Mw value, the more likely it is that low molecular weight components are contained, and the larger the Mp / Mw value, the more likely it is that high molecular weight components are contained. Note that when two or more peaks are present in the GPC chart, the molecular weight corresponding to the largest peak is taken as the peak top molecular weight (Mp).

[0043] In the present invention, the number-average molecular weight (Mn), weight-average molecular weight (Mw), Z-average molecular weight (Mz), ratio of weight-average molecular weight to number-average molecular weight (Mw / Mn), ratio of Z-average molecular weight to weight-average molecular weight (Mz / Mw), and ratio of peak-top molecular weight (Mp) to weight-average molecular weight (Mw) of the hydrocarbon resin (Mp / Mw) can be adjusted by the type and amount of monomer used in polymerization and the polymerization conditions. In particular, the ratio of peak-top molecular weight (Mp) to weight-average molecular weight (Mw) of the hydrocarbon resin (Mp / Mw) can be controlled by an appropriate combination of the type and amount of monomer used in polymerization, the amount of polymerization catalyst used, the polymerization temperature, and the mixing temperature and mixing time when the polymerization catalyst is mixed in a volatile solvent in advance. For example, the ratio of peak-top molecular weight (Mp) to weight-average molecular weight (Mw) of the hydrocarbon resin (Mp / Mw) tends to decrease as the amount of polymerization catalyst used increases and the polymerization temperature increases. Furthermore, the shorter the mixing time when the polymerization catalyst is mixed in advance with the volatile solvent, the smaller the ratio (Mp / Mw) of the peak top molecular weight (Mp) to the weight average molecular weight (Mw) of the hydrocarbon resin tends to be.

[0044] The softening point of the hydrocarbon resin used in the present invention is in the range of 80 to 150°C, preferably in the range of 85 to 145°C, more preferably in the range of 90 to 140°C, even more preferably in the range of 90 to 115°C, and particularly preferably in the range of 92 to 105°C. By setting the softening point within the above range, it is possible to improve compatibility with diene rubber, thereby appropriately improving the rolling resistance, wet grip performance, and low-temperature performance of the obtained cross-linked rubber. The softening point of the hydrocarbon resin can be measured in accordance with JIS K6863.

[0045] <Method for Producing Hydrocarbon Resin> The method for producing the hydrocarbon resin used in the present invention is not particularly limited, but examples thereof include a method of subjecting a monomer mixture for constituting the hydrocarbon resin to addition polymerization, and a preferred example thereof is a method of addition polymerization using a Friedel-Crafts type cationic polymerization catalyst.

[0046] The Friedel-Crafts type cationic polymerization catalyst is not particularly limited, but examples thereof include halides of aluminum, iron, tantalum, zirconium, tin, beryllium, boron, antimony, gallium, bismuth, molybdenum, etc. Among these, aluminum chloride (AlCl ３ ) and aluminum bromide (AlBr ３ The amount of the Friedel-Crafts cationic polymerization catalyst used is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, still more preferably 0.5 to 2.0 parts by mass, and particularly preferably 0.7 to 1.7 parts by mass, per 100 parts by mass of the monomer mixture used in the polymerization.

[0047] During polymerization, a halogenated hydrocarbon may be used in addition to the Friedel-Crafts type cationic polymerization catalyst, since this allows for further enhancement of catalytic activity.

[0048] Specific examples of halogenated hydrocarbons include halogenated hydrocarbons in which a halogen atom is bonded to a tertiary carbon atom, such as t-butyl chloride, t-butyl bromide, 2-chloro-2-methylbutane, and triphenylmethyl chloride; and halogenated hydrocarbons in which a halogen atom is bonded to a carbon atom adjacent to a carbon-carbon unsaturated bond, such as benzyl chloride, benzyl bromide, (1-chloroethyl)benzene, allyl chloride, 3-chloro-1-propyne, 3-chloro-1-butene, 3-chloro-1-butyne, and cinnamic chloride. Among these, t-butyl chloride and benzyl chloride are preferred from the viewpoint of achieving an excellent balance between catalytic activity and ease of handling. The halogenated hydrocarbons may be used alone or in combination of two or more. The amount of halogenated hydrocarbon used, expressed as a molar ratio relative to the Friedel-Crafts cationic polymerization catalyst, is preferably in the range of 0.05 to 50, more preferably 0.1 to 10.

[0049] Furthermore, from the viewpoint of better controlling the polymerization reaction, it is preferable to carry out the polymerization reaction by adding a volatile solvent to the polymerization reaction system. The type of volatile solvent is not particularly limited as long as it does not inhibit the polymerization reaction, but saturated aliphatic hydrocarbons or aromatic hydrocarbons are preferred. Examples of saturated aliphatic hydrocarbons include chain saturated aliphatic hydrocarbons having 5 to 10 carbon atoms, such as n-pentane, n-hexane, 2-methylpentane, 3-methylpentane, n-heptane, 2-methylhexane, 3-methylhexane, 3-ethylpentane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4-dimethylpentane, 3,3-dimethylpentane, 2,2,3-trimethylbutane, and 2,2,4-trimethylpentane; and cyclic saturated aliphatic hydrocarbons having 5 to 10 carbon atoms, such as cyclopentane, cyclohexane, cycloheptane, and cyclooctane. Examples of aromatic hydrocarbons include aromatic hydrocarbons having 6 to 10 carbon atoms, such as benzene, toluene, and xylene. The volatile solvent may be used alone or in combination of two or more. The amount of the volatile solvent used is not particularly limited, but is preferably 10 to 1,000 parts by mass, more preferably 50 to 500 parts by mass, per 100 parts by mass of the monomer mixture used in the polymerization.

[0050] In carrying out the polymerization reaction, the order in which the monomer mixture and the polymerization catalyst components are added to a polymerization reactor is not particularly limited, and they may be added in any order. However, from the viewpoint of favorably controlling the polymerization reaction and controlling the ratio (Mp / Mw) of the peak top molecular weight (Mp) to the weight average molecular weight (Mw), a method is preferred in which the polymerization catalyst is added to a volatile solvent in advance and mixed to make the polymerization catalyst dispersed in the volatile solvent, and then the monomer mixture is added to the polymerization reactor to start the polymerization reaction.

[0051] When the polymerization catalyst is added in advance to the volatile solvent and mixed, it is preferable to set conditions such that aggregates of the polymerization catalyst partially remain in the volatile solvent. The mixing temperature is preferably 45 to 80°C, more preferably 50 to 70°C, and the mixing time is preferably 10 seconds to 4 minutes, more preferably 30 seconds to 3 minutes.

[0052] The polymerization temperature when carrying out the polymerization reaction is not particularly limited, but is preferably 50 to 90° C., more preferably 55 to 85° C., and even more preferably 60 to 78° C. The polymerization reaction time may be appropriately selected, but is usually 10 minutes to 12 hours, and preferably 30 minutes to 6 hours.

[0053] The polymerization reaction can be terminated by adding a polymerization terminator such as methanol, an aqueous sodium hydroxide solution, or an aqueous ammonia solution to the polymerization reaction system when a desired polymerization conversion rate is achieved, thereby obtaining a polymer solution containing the hydrocarbon resin.

[0054] After the polymerization, a polymerization terminator may be added to inactivate the polymerization catalyst, and the resulting catalyst residue insoluble in the solvent may be removed by filtration or the like.

[0055] After the polymerization, it is preferable to remove volatile organic compound components such as the solvent, unreacted monomers, and low-molecular-weight oligomer components from the polymer solution containing the hydrocarbon resin by steam distillation or the like.

[0056] If necessary, the obtained hydrocarbon resin may be subjected to a hydrogenation reaction to hydrogenate the carbon-carbon double bonds in the hydrocarbon resin, thereby forming a hydrogenated product. That is, the hydrocarbon resin may be a hydrogenated product. The hydrogenation of the hydrocarbon resin may be carried out by contacting the hydrocarbon resin with hydrogen in the presence of a hydrogenation catalyst.

[0057] The hydrogenation catalyst is not particularly limited, but a nickel catalyst is preferred. In particular, from the viewpoint of high reactivity, a catalyst containing, as a main component, a compound in which metal nickel is supported on a supported inorganic compound as a support is preferred. Specific examples of the supported inorganic compound as a support include silica, alumina, boria, silica-alumina, diatomaceous earth, clay, clay, magnesia, magnesia-silica (silica-magnesium oxide), titania, and zirconia. Of these, magnesia-silica is preferred from the viewpoint of reactivity.

[0058] <Diene-Based Rubber> The rubber composition of the present invention contains a diene-based rubber in addition to the hydrocarbon resin described above. The diene-based rubber is not particularly limited as long as it can be blended with the hydrocarbon resin. Examples of such diene-based rubber include the diene-based rubbers described in JP 2015-189873 A. Specific examples include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), and ethylene-propylene-diene terpolymer (EPDM). Among these, styrene-butadiene copolymer rubber and butadiene rubber are preferred, with styrene-butadiene copolymer rubber being more preferred. The Mooney viscosity (ML1+4, 100°C) of the diene-based rubber is not particularly limited, but is preferably 20 to 90, and more preferably 30 to 80. When the diene-based rubber is an oil-extended rubber, the Mooney viscosity of the oil-extended rubber is preferably within the above range. Furthermore, the glass transition temperature (Tg) of the diene rubber is not particularly limited, but is preferably −110° C. to 20° C., and more preferably −90° C. to 0° C. By using such a rubber as the diene rubber, the cross-linked rubber can be made to have an excellent balance of rolling resistance, wet grip performance, and low temperature performance. The diene rubber may be used alone or in combination of two or more types.

[0059] The diene rubber used in the present invention is not particularly limited in terms of molecular weight or microstructure, and may be terminally modified with amine, amide, silyl, alkoxysilyl, carboxyl, or hydroxyl groups, or may be epoxidized. The diene rubber used in the present invention may be hydrogenated, but is preferably non-hydrogenated. When a diene rubber containing butadiene units, such as a styrene-butadiene copolymer rubber or a butadiene rubber, is used as the diene rubber, the butadiene unit content in the diene rubber is preferably 30% by mass or more, more preferably 50% by mass or more, and the vinyl bond content in the butadiene units is not particularly limited, but is preferably 1 to 90%, more preferably 3 to 85%, and even more preferably 5 to 80%.

[0060] The blending ratio of the diene rubber to the hydrocarbon resin in the rubber composition of the present invention may be such that 1 to 200 parts by mass of the hydrocarbon resin is blended per 100 parts by mass of the diene rubber, preferably 1 to 70 parts by mass, more preferably 3 to 35 parts by mass, and even more preferably 15 to 25 parts by mass. If the blending amount of the hydrocarbon resin is too small, the resulting cross-linked rubber will be inferior in wet grip performance and low-temperature performance, while if it is too large, the resulting cross-linked rubber will be inferior in rolling resistance.

[0061] The rubber composition of the present invention may consist solely of a diene rubber and the hydrocarbon resin, but may also contain other components. Examples of other components that may be contained in the rubber composition of the present invention include fillers, silane coupling agents, crosslinking agents, crosslinking accelerators, crosslinking activators, antioxidants, antioxidants, activators, process oils, plasticizers, lubricants, and tackifiers, and these other compounding agents may be compounded in the required amounts, respectively.

[0062] Fillers that can be compounded in the rubber composition of the present invention include those that are commonly used in rubber compositions, and examples thereof include inorganic hollow fillers such as carbon black, clay, diatomaceous earth, silica, talc, barium sulfate, calcium carbonate, magnesium carbonate, metal oxides, mica, aluminum hydroxide, various metal powders, wood powder, glass powder, ceramic powder, glass balloons, and silica balloons; and organic hollow fillers such as polystyrene, polyvinylidene fluoride, and polyvinylidene fluoride copolymers.

[0063] Examples of silica include dry process white carbon, wet process white carbon, colloidal silica, and precipitated silica. Among these, wet process white carbon, which is mainly composed of hydrous silicic acid, is preferred. Carbon-silica dual phase filler, in which silica is supported on the surface of carbon black, may also be used. These silicas may be used alone or in combination of two or more. The nitrogen adsorption specific surface area (measured by the BET method in accordance with ASTM D3037-81) of the silica used is preferably 100 to 400 m ２ / g, more preferably 150 to 350 m ２ The pH of the silica is preferably 5 to 10.

[0064] The amount of silica compounded in the rubber composition of the present invention is preferably 10 to 200 parts by mass, more preferably 20 to 150 parts by mass, and even more preferably 30 to 75 parts by mass, per 100 parts by mass of the rubber component in the rubber composition. By setting the amount of silica compounded within the above range, the obtained cross-linked rubber product can be made to have even better rolling resistance, wet grip performance, and low-temperature performance.

[0065] When silica is used as a filler, it is preferable to use a silane coupling agent in combination. Examples of silane coupling agents include vinyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, 3-octathio-1-propyl-triethoxysilane, bis(3-(triethoxysilyl)propyl)disulfide, bis(3-(triethoxysilyl)propyl)tetrasulfide, γ-trimethoxysilylpropyldimethylthiocarbamyltetrasulfide, and γ-trimethoxysilylpropylbenzothiazyltetrasulfide. These silane coupling agents can be used alone or in combination of two or more. The amount of silane coupling agent added is preferably 0.1 to 30 parts by mass, more preferably 1 to 15 parts by mass, per 100 parts by mass of silica.

[0066] Examples of carbon black include furnace black, acetylene black, thermal black, channel black, and graphite. These carbon blacks can be used alone or in combination of two or more. The amount of carbon black added is usually 120 parts by mass or less per 100 parts by mass of the rubber component in the rubber composition.

[0067] The filler may be used alone or in combination of two or more kinds. For example, a mixture of silica and carbon black may be used as the filler.

[0068] The content of fillers other than silica and carbon black may be within a range in which the effects of the present invention can be obtained, and for example, can be 120 parts by mass or less per 100 parts by mass of the rubber component in the rubber composition.

[0069] The crosslinking agent is not particularly limited, but examples thereof include sulfur, sulfur halides, organic peroxides, quinone dioximes, organic polyamine compounds, and alkylphenol resins having methylol groups. Of these, sulfur is preferably used. The amount of crosslinking agent blended is preferably 0.1 to 15 parts by mass, more preferably 0.5 to 5 parts by mass, and particularly preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component in the rubber composition.

[0070] When sulfur or a sulfur-containing compound is used as the crosslinking agent, it is preferable to use a crosslinking accelerator and a crosslinking activator in combination. Examples of crosslinking accelerators include sulfenamide-based crosslinking accelerators; guanidine-based crosslinking accelerators; thiourea-based crosslinking accelerators; thiazole-based crosslinking accelerators; thiuram-based crosslinking accelerators; dithiocarbamic acid-based crosslinking accelerators; and xanthogenic acid-based crosslinking accelerators. Among these, those containing sulfenamide-based crosslinking accelerators are preferred. These crosslinking accelerators may be used alone or in combination of two or more. The amount of crosslinking accelerator blended is preferably 0.1 to 15 parts by mass, more preferably 0.5 to 5 parts by mass, and particularly preferably 1 to 4 parts by mass, per 100 parts by mass of the rubber component in the rubber composition.

[0071] Examples of crosslinking activators include higher fatty acids such as stearic acid, zinc oxide, etc. These crosslinking activators may be used alone or in combination of two or more. The amount of crosslinking activator blended is preferably 0.05 to 20 parts by mass, and particularly preferably 0.5 to 15 parts by mass, per 100 parts by mass of the rubber component in the rubber composition.

[0072] If desired, the rubber composition of the present invention may contain an antioxidant such as an amine-based stabilizer, a phenol-based stabilizer, a phosphorus-based stabilizer, or a sulfur-based stabilizer. The amount of antioxidant added may be determined appropriately depending on the type of antioxidant.

[0073] Furthermore, an antioxidant may be added to the rubber composition of the present invention as needed. Examples of antioxidants include, but are not limited to, hindered phenol compounds such as pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2,6-di-t-butyl-p-cresol, and di-t-butyl-4-methylphenol; thiodicarboxylate esters such as dilauryl thiopropionate; and phosphites such as tris(nonylphenyl)phosphite. The antioxidants may be used alone or in combination of two or more. The content of the antioxidant is not particularly limited, but is preferably 10 parts by mass or less, and more preferably 0.05 to 5 parts by mass, per 100 parts by mass of the rubber component in the rubber composition.

[0074] In addition, the rubber composition of the present invention may contain a resin other than the diene rubber and the hydrocarbon resin. By incorporating a resin, it is possible to impart tackiness to the rubber composition and improve the dispersibility of fillers in the rubber composition. As a result, further improvements in the rolling resistance, wet grip performance, and low-temperature performance of the resulting cross-linked rubber can be expected. Furthermore, similar to the effect of a plasticizer, it can also improve the processability of the rubber composition. Examples of resins include C9 petroleum resins, dicyclopentadiene resins, terpene resins, terpene phenol resins, aromatic-modified terpene resins, alkylphenol-acetylene resins, rosin resins, rosin ester resins, indene resins, C9 resins containing indene, α-methylstyrene-indene copolymer resins, coumarone-indene resins, farnesene resins, and polylimonene resins. These resins may be modified or hydrogenated. These resins may be used alone or in combination of two or more. The amount of resin incorporated is preferably 25 parts by mass or less per 100 parts by mass of the rubber component in the rubber composition.

[0075] The rubber composition of the present invention can be produced by kneading the components according to conventional methods. For example, the components excluding thermally unstable components such as crosslinking agents and crosslinking accelerators are kneaded with a diene rubber and a hydrocarbon resin, and then the resulting mixture is kneaded with thermally unstable components such as a crosslinking agent and a crosslinking accelerator to obtain the desired rubber composition. The kneading temperature when kneading the components excluding thermally unstable components with the diene rubber and the hydrocarbon resin is preferably 80 to 200°C, more preferably 120 to 180°C, and the kneading time is preferably 30 seconds to 30 minutes. The kneading of the kneaded mixture with the thermally unstable components is preferably carried out after cooling to 100°C or less, more preferably 80°C or less.

[0076] By using the rubber composition of the present invention, it is possible to obtain a cross-linked rubber product that has an excellent balance of rolling resistance, wet grip performance, and low-temperature performance. Taking advantage of these properties, the rubber composition of the present invention is preferably used as a material for various tire parts such as the tread (cap tread, base tread), carcass, sidewall, and bead portion of a tire, and among these, it can be suitably used for various tire parts such as the tread, carcass, sidewall, and bead portion of various tires such as all-season tires, high-performance tires, and studless tires, and can be particularly suitably used for, for example, tire treads, and among these, it is particularly preferred to use it for cap treads.

[0077] <Rubber Cross-Linked Product> The cross-linked rubber product of the present invention is obtained by cross-linking the rubber composition of the present invention described above. The cross-linked rubber product of the present invention can be produced by using the rubber composition of the present invention, for example, molding it into a desired shape using a molding machine such as an extruder, injection molding machine, compressor, or roll, and then heating it to cause a cross-linking reaction, thereby fixing the shape as a cross-linked rubber product. In this case, cross-linking may be carried out after molding in advance, or simultaneously with molding. The molding temperature is usually 10 to 200°C, preferably 25 to 120°C. The cross-linking temperature is usually 100 to 200°C, preferably 130 to 190°C, and the cross-linking time is usually 1 minute to 24 hours, preferably 2 minutes to 12 hours, and particularly preferably 3 minutes to 6 hours.

[0078] Depending on the shape, size, etc. of the cross-linked rubber product, even if the surface is cross-linked, the inside may not be sufficiently cross-linked, so secondary cross-linking may be carried out by further heating.

[0079] The heating method may be appropriately selected from common methods used for crosslinking rubber compositions, such as press heating, steam heating, oven heating, and hot air heating.

[0080] The cross-linked rubber product of the present invention thus obtained is obtained using the rubber composition of the present invention described above, and therefore has an excellent balance of rolling resistance, wet grip performance, and low-temperature performance.

[0081] Taking advantage of its excellent rolling resistance, wet grip performance and low-temperature performance, the cross-linked rubber product of the present invention is preferably used, for example, in tires as a material for various tire portions such as treads (cap treads and base treads), carcasses, sidewalls and bead portions, and among these, it can be suitably used in various tire portions such as treads, carcasses, sidewalls and bead portions in various tires such as all-season tires, high-performance tires and studless tires, and can be particularly suitably used, for example, for tire treads, and among these, it is particularly preferred to use it for cap treads.

[0082] Next, the pneumatic tire of the present invention will be described. The pneumatic tire of the present invention is characterized in that the above-mentioned rubber composition is used in the tread.

[0083] The tread uses the above-mentioned rubber composition, i.e., is formed using the above-mentioned rubber composition, and usually contains the cross-linked rubber of the present invention obtained by cross-linking the above-mentioned rubber composition of the present invention.

[0084] The pneumatic tire may have a tread formed using the rubber composition, and other portions thereof may also be formed using the rubber composition.

[0085] The tread formed using the rubber composition may be a part of the tread or the entire tread, but preferably includes at least a cap tread.

[0086] Furthermore, the method for manufacturing the pneumatic tire of the present invention may be any method that can manufacture a pneumatic tire having a tread formed using the above composition, and any known method for manufacturing a pneumatic tire may be used.

[0087] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. Note that "parts" and "%" are by mass unless otherwise specified. The test methods used in these examples and comparative examples are as follows.

[0088] [Number-average molecular weight (Mn), weight-average molecular weight (Mw), Z-average molecular weight (Mz), peak-top molecular weight (Mp), molecular weight distribution (Mw / Mn, Mz / Mw), and ratio (Mp / Mw) of weight-average molecular weight (Mw) to peak-top molecular weight (Mp) of hydrocarbon resin] The hydrocarbon resin was analyzed by gel permeation chromatography to determine the number-average molecular weight (Mn), weight-average molecular weight (Mw), Z-average molecular weight (Mz), and peak-top molecular weight (Mp) in terms of standard polystyrene. Based on these results, the molecular weight distribution (Mw / Mn, Mz / Mw) and the ratio (Mp / Mw) of weight-average molecular weight (Mw) to peak-top molecular weight (Mp) were also determined. The gel permeation chromatography analysis was performed using a measuring device "HLC-8320GPC" manufactured by Tosoh Corporation and a column consisting of three connected "TSKgel SuperMultipore HZ" manufactured by Tosoh Corporation, using tetrahydrofuran as a solvent at 40°C and a flow rate of 1.0 mL / min.

[0089] [Softening Point of Hydrocarbon Resin] The softening point of the hydrocarbon resin was measured in accordance with JIS K6863.

[0090] [Mooney viscosity (ML1+4) of rubber composition] The Mooney viscosity (ML1+4) of the rubber composition was measured in accordance with JIS K 6300-1:2001 under the following conditions. The smaller the Mooney viscosity value, the better the processability. Test temperature: 100°C Rotor type: L-type Testing machine used: Shimadzu Mooney Viscometer SMV-300J manufactured by Shimadzu Corporation

[0091] [Tensile strength (MPa) and elongation (%) of cross-linked rubber product] For test pieces of the cross-linked rubber product as samples, the tensile strength (MPa) and elongation (%) were measured under the following conditions in accordance with JIS K 6251:2010. It can be determined that the larger the values, the better the tensile strength and elongation. - Test piece preparation method: Sheet prepared by press cross-linking, then punched out - Test piece shape: Dumbbell No. 3 - Test piece collection direction: Parallel to grain - Number of test pieces: 3 - Measurement temperature: 23°C - Test speed: 500 mm / min - Testing machine used: TENSOMETER 10k manufactured by ALPHA TECHNOLOGIES - Testing machine capacity: Load cell type 1 kN

[0092] [Storage modulus E' at -25°C] For test pieces of the cross-linked rubber samples, the storage modulus E' at -25°C was measured in accordance with JIS K 7244-4 under the following measurement conditions: dynamic strain of 0.5% and 10 Hz. With regard to this property, Example 1 and Comparative Examples 1 and 2 are shown as indexes with Comparative Example 1 (reference sample) set to 100, and Examples 2 to 4 and Comparative Examples 3 to 5 are shown as indexes with Comparative Example 3 (reference sample) set to 100. It can be determined that the lower the storage modulus E' at -25°C, the more excellent the low-temperature performance. Measurement item: Dynamic storage modulus E' Sample preparation method: Punched from sheet Specimen shape: Length 50 mm x Width 2 mm x Thickness 2 mm Number of test pieces: 1 Clamp distance: 20 mm

[0093] [Loss Tangent tanδ] For test pieces of the cross-linked rubber sample, the loss tangent tanδ at 0°C under conditions of a dynamic strain of 0.5% and 10 Hz, and the loss tangent tanδ at 60°C under conditions of a dynamic strain of 2.0% and 10 Hz were measured in accordance with JIS K 7244-4 under the following measurement conditions. With regard to these properties, Example 1 and Comparative Examples 1 and 2 are expressed as indexes with Comparative Example 1 (reference sample) set to 100, and Examples 2 to 4 and Comparative Examples 3 to 5 are expressed as indexes with Comparative Example 3 (reference sample) set to 100. It can be determined that the higher the loss tangent tanδ at 0°C, the better the wet grip performance, and the lower the loss tangent tanδ at 60°C, the better the rolling resistance (the lower the loss tangent tanδ at 60°C, the lower the rolling resistance). Measurement items: Dynamic storage modulus E': Dynamic loss modulus E": Loss tangent tan δ Sample preparation method: Punched from sheet Test piece shape: Length 50 mm x Width 2 mm x Thickness 2 mm Number of test pieces: 1 Clamp distance: 20 mm

[0094] Example 1 (Production of Hydrocarbon Resin) A polymerization reactor was charged with 52.7 parts of cyclopentane as a hydrocarbon solvent and heated to 70°C. Then, 1.0 part of aluminum chloride as a polymerization catalyst was added. While maintaining the temperature (70°C), the mixture was mixed for 2 minutes to disperse the aluminum chloride in the cyclopentane while leaving some aggregates. After the 2-minute mixing period, a mixture consisting of 48.2 parts of 1,3-pentadiene, 0.3 parts of isoprene, 17.0 parts of cyclopentene, 33.0 parts of isobutylene, 1.0 part of diisobutylene, 0.3 parts of dicyclopentadiene, 0.2 parts of C4-C6 unsaturated hydrocarbons, 15.8 parts of C4-C6 saturated hydrocarbons, and 0.1 parts of toluene was continuously added to the polymerization reactor over a 60-minute period while maintaining the temperature (70°C), thereby conducting polymerization. Thereafter, aqueous sodium hydroxide solution was added to the polymerization reactor to terminate the polymerization reaction. The types and amounts of components in the polymerization reactor during the polymerization reaction are summarized in Table 1. The precipitate formed upon termination of the polymerization was removed by filtration to obtain a polymer solution containing a hydrocarbon resin and unreacted monomers. The polymer solution was then charged into a distillation still and heated under a nitrogen atmosphere to remove the polymerization solvent and unreacted monomers, yielding a hydrocarbon resin. Because the amount of unreacted monomer was extremely small, the monomer composition constituting the obtained hydrocarbon resin was determined to be substantially the same as the monomer composition used in the polymerization (the same applies to Examples 2 to 4 and Comparative Examples 1 to 5 described below). The number-average molecular weight (Mn), weight-average molecular weight (Mw), Z-average molecular weight (Mz), peak-top molecular weight (Mp), molecular weight distribution (Mw / Mn, Mz / Mw), ratio of weight-average molecular weight (Mw) to peak-top molecular weight (Mp) (Mp / Mw), and softening point of the obtained hydrocarbon resin were measured according to the methods described above. The results are shown in Table 1.

[0095] (Production of Rubber Composition) In a Banbury mixer, 100 parts of solution-polymerized styrene-butadiene rubber (SBR) (trade name "Nipol NS612", manufactured by ZS Elastomers, styrene monomer unit content 15% by weight, vinyl bond content in butadiene unit portion 30%, Mooney viscosity (ML1+4, 100°C) 62, glass transition temperature (Tg) -65°C, no extender oil) was masticated for 30 seconds, and then silica (trade name "Nipsil" manufactured by Tosoh Silica Corporation) was added. A mixture of 46.6 parts of carbon black (manufactured by Cabot Japan Corporation, trade name "N339"), 5 parts of a silane coupling agent: bis(3-(triethoxysilyl)propyl)tetrasulfide (manufactured by Tegussa, trade name "Si69"), and 20 parts of the hydrocarbon resin obtained above was added and kneaded for 90 seconds, followed by addition of 23.4 parts of silica (manufactured by Rhodia, trade name "Zeosil 1165MP"), 3 parts of zinc oxide, 2 parts of stearic acid, and 2 parts of an antioxidant: N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., trade name "Nocrac 6C"), and kneading for a further 90 seconds. Subsequently, 10 parts of process oil (manufactured by Nippon Oil Corporation, trade name "Aromax T-DAE") was added. Thereafter, the mixture was kneaded (primary kneading) for 60 seconds or more at 145 to 155°C starting from 90°C, and then the kneaded mixture was discharged from the mixer.

[0096] The obtained kneaded product was cooled to room temperature, and then kneaded again in the Banbury mixer at a starting temperature of 90°C for 2 minutes (secondary kneading), and then the kneaded product was discharged from the mixer. The temperature of the kneaded product at the end of kneading was 145°C.

[0097] Next, 1.7 parts of sulfur, 1.8 parts of a crosslinking accelerator: N-cyclohexyl-2-benzothiazolylsulfenamide (CBS, trade name "Noccela CZ-G", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), and 1.7 parts of diphenylguanidine (DPG, trade name "Noccela D", manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were added to the resulting kneaded mixture using two rolls at 50°C, and after kneading (crosslinking agent kneading), a sheet-like rubber composition was taken out. The Mooney viscosity (ML1+4) of the resulting rubber composition was then measured. The results are shown in Table 2. The kneading conditions for the primary kneading, secondary kneading, and crosslinking agent kneading were as follows:

[0098] (Mixing conditions for primary and secondary mixing) Testing machine: Laboplastomill Banbury type mixer B-600 manufactured by Toyo Seiki Seisakusho, Ltd. Filling rate: 70 to 75 vol% Rotor rotation speed: 50 rpm Test start temperature setting: 90°C

[0099] (Kneading conditions for kneading crosslinking agent) Testing machine: Electrically heated high-temperature roll machine manufactured by Ikeda Kikai Kogyo Co., Ltd. Roll size: 6φ×16 Front roll rotation speed: 24 rpm Front and rear roll rotation ratio: 1:1.22 Roll temperature: 50±5°C Number of turns: 2 times each on the left and right Rolling width: Roll spacing approximately 0.8 mm Number of times rolled: 5 times

[0100] (Production of Cross-Linked Rubber Product) The rubber composition obtained above was press-cross-linked for 40 minutes at a press pressure of about 8 MPa and a press temperature of 160°C, and then further aged overnight in a thermostatic chamber at 23°C, after which a test piece of the cross-linked rubber product measuring 150 mm x 150 mm x 2 mm thick was prepared. The cross-linked rubber product obtained was subjected to measurements of tensile strength (MPa), elongation (%), storage modulus E' at -25°C, and loss tangent tanδ (0°C, 60°C). The results are shown in Table 2.

[0101] Comparative Examples 1 and 2 (Production of Hydrocarbon Resins) Hydrocarbon resins of Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the types and amounts of components added to the polymerization reactor, the mixing temperature and mixing time when mixing aluminum chloride as a polymerization catalyst, and the polymerization temperature were changed as shown in Table 1 below. The obtained hydrocarbon resins were then measured in the same manner as in Example 1. The results are shown in Table 1.

[0102] (Production of Rubber Composition and Cross-Linked Rubber Product) Except for using the hydrocarbon resin obtained above, a rubber composition and a cross-linked rubber product were obtained and measured in the same manner as in Example 1. The results are shown in Table 2.

[0103]

[0104]

[0105] Examples 2 to 4 (Production of Hydrocarbon Resins) The hydrocarbon resins of Examples 2 to 4 were obtained in the same manner as in Example 1, except that the types and amounts of components added to the polymerization reactor, the mixing temperature and mixing time when mixing aluminum chloride as a polymerization catalyst, and the polymerization temperature were changed as shown in Table 3 below. The C9 fraction and styrene not described in Example 1 were mixed with 1,3-pentadiene and the like and subjected to polymerization. The C9 fraction mainly contained styrene, α-methylstyrene, β-methylstyrene, vinyltoluene, and indene as aromatic monomers, and the amounts used in Table 3 are shown in terms of aromatic monomers. The obtained hydrocarbon resins were then measured in the same manner as in Example 1. The results are shown in Table 3.

[0106] (Production of Rubber Composition and Cross-Linked Rubber Product) Except for using the hydrocarbon resin obtained above, a rubber composition and a cross-linked rubber product were obtained and measured in the same manner as in Example 1. The results are shown in Table 4.

[0107] Comparative Examples 3 to 5 (Production of Hydrocarbon Resins) The hydrocarbon resins of Comparative Examples 3 to 5 were obtained in the same manner as in Example 1, except that the types and amounts of components added to the polymerization reactor, the mixing temperature and mixing time when mixing aluminum chloride as a polymerization catalyst, and the polymerization temperature were changed as shown in Table 3 below. The C9 fraction and styrene not described in Example 1 were mixed with 1,3-pentadiene and the like and subjected to polymerization. The C9 fraction mainly contained styrene, α-methylstyrene, β-methylstyrene, vinyltoluene, and indene as aromatic monomers, and the amounts used in Table 3 are shown in terms of aromatic monomers. The obtained hydrocarbon resins were then measured in the same manner as in Example 1. The results are shown in Table 3.

[0108] (Production of Rubber Composition and Cross-Linked Rubber Product) Except for using the hydrocarbon resin obtained above, a rubber composition and a cross-linked rubber product were obtained and measured in the same manner as in Example 1. The results are shown in Table 4.

[0109]

[0110]

[0111] From the results of Example 1 and Comparative Examples 1 and 2 shown in Tables 1 and 2, and the results of Examples 2 to 4 and Comparative Examples 3 to 5 shown in Tables 3 and 4, it was found that when a rubber composition was blended with a hydrocarbon resin having a number average molecular weight (Mn), weight average molecular weight (Mw), Z average molecular weight (Mz), ratio of weight average molecular weight to number average molecular weight (Mw / Mn), ratio of Z average molecular weight to weight average molecular weight (Mz / Mw), and softening point within the ranges specified in the present invention, and a ratio of peak top molecular weight (Mp) to weight average molecular weight (Mw) (Mp / Mw) in the range of 0.4 to 0.8, the cross-linked rubber obtained using this had a low storage modulus E' at -25°C and excellent low temperature performance, a high loss tangent tanδ at 0°C and excellent wet grip performance, and further had a low loss tangent tanδ at 60°C and low rolling resistance, and was excellent in balance of low temperature performance, wet grip performance, and rolling resistance (Examples 1 to 4). On the other hand, when a hydrocarbon resin having a ratio (Mp / Mw) of peak top molecular weight (Mp) to weight average molecular weight (Mw) of more than 0.8 was used, the resulting cross-linked rubber product had a high storage modulus E' at -25°C, poor low temperature performance, a low loss tangent tan δ at 0°C, and poor wet grip performance (Comparative Examples 1 to 3, 5). Furthermore, when a hydrocarbon resin having an excessively high ratio (Mz / Mw) of Z average molecular weight to weight average molecular weight was used, the resulting cross-linked rubber product had a low loss tangent tan δ at -0°C, poor wet grip performance, a high loss tangent tan δ at 60°C, and high rolling resistance (Comparative Example 4).

Claims

1. A rubber composition containing a diene rubber and a hydrocarbon resin, the content of the hydrocarbon resin is 1 to 200 parts by mass based on 100 parts by mass of the diene rubber, The hydrocarbon resin is Contains aliphatic monomer units, or aliphatic and aromatic monomer units; The number average molecular weight (Mn) is in the range of 400 to 3000; The weight average molecular weight (Mw) is in the range of 700 to 6000; The Z-average molecular weight (Mz) is in the range of 1,500 to 20,000; The ratio of the weight average molecular weight to the number average molecular weight (Mw / Mn) is in the range of 1.0 to 4.0; The ratio of the Z-average molecular weight to the weight-average molecular weight (Mz / Mw) is in the range of 1.0 to 3.5; The ratio (Mp / Mw) of the peak top molecular weight (Mp) to the weight average molecular weight (Mw) is in the range of 0.4 to 0.8; The softening point temperature is in the range of 80 to 150°C. Rubber composition.

2. The hydrocarbon resin is 1 to 70 mass% of 1,3-pentadiene monomer units, 1 to 30% by mass of alicyclic monoolefin monomer units having 4 to 6 carbon atoms, 0 to 15% by mass of isoprene monomer units, 0 to 50% by mass of acyclic monoolefin monomer units having 4 to 8 carbon atoms, 0 to 10% by weight of alicyclic diolefin monomer units, and Contains 0 to 40 mass % of aromatic monoolefin monomer units; The rubber composition according to claim 1.

3. 3. The rubber composition according to claim 1, wherein the hydrocarbon resin is a hydrogenated product.

4. The rubber composition according to claim 1 or 2, further comprising a filler.

5. The rubber composition according to claim 1 or 2, further comprising a crosslinking agent.

6. 3. The rubber composition according to claim 1, wherein the diene rubber comprises a styrene-butadiene copolymer rubber or a butadiene rubber.

7. A cross-linked rubber product obtained by cross-linking the rubber composition according to claim 1 or 2.

8. A pneumatic tire using the cross-linked rubber according to claim 7 in its tread.