JP7296772B2 - Rubber composition and pneumatic tire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rubber composition and a pneumatic tire comprising the rubber composition.

In general, tires are used in various driving environments, and are required to improve wet grip performance (hereinafter simply referred to as "WET performance"), which is grip performance on wet road surfaces, for example, in the rain. However, when a rubber composition is designed for the purpose of improving such WET performance, the fuel efficiency of the resulting vulcanized rubber may deteriorate, so a technique for improving these in a well-balanced manner has been desired. .

In Patent Document 1 below, a rubber composition containing at least two diene rubbers having a bimodal temperature distribution curve of tan δ as a rubber component is used as a raw material to improve WET performance and fuel efficiency of a pneumatic tire. Techniques for improvement are described.

Further, in Patent Document 2 below, a rubber composition containing a predetermined amount of at least one selected from homopolymer resins and copolymer resins of aromatic vinyl compounds having a softening point of 140° C. or higher is used as a raw material. Thus, a technique for improving the initial grip performance and running stability of the tire is described.

Furthermore, in Patent Document 3 below, rubber containing a liquid copolymer containing an aromatic vinyl compound and a conjugated diene-containing compound as monomer units and having a weight average molecular weight (Mw) of 1,000 to 50,000 A technique for improving WET performance and fuel efficiency of a pneumatic tire by using the composition as a raw material is described.

JP-A-08-27313 JP 2008-169295 A JP 2016-117880 A

In order to achieve both WET performance and fuel efficiency of a pneumatic tire, it is important to optimize the loss tangent (tan δ) of the rubber composition as a raw material. In general, WET performance greatly depends on tan δ at 0° C. of the raw material rubber composition (hereinafter also referred to as “tan δ (0° C.)”), and the larger tan δ (0° C.) is the WET performance of the pneumatic tire. Excellent for On the other hand, low fuel consumption greatly depends on tan δ at 60° C. of the raw material rubber composition (hereinafter also referred to as “tan δ (60° C.)”), and the smaller the tan δ (60° C.), the lower the pneumatic tire. Excellent fuel efficiency.

However, with the technology described in the above patent document, it is difficult to increase the tan δ (0 ° C.) of the rubber composition and to decrease the tan δ (60 ° C.), and the WET performance and fuel efficiency of the pneumatic tire as the final product It turned out to be difficult to improve the properties in a well-balanced manner. The present invention was completed in view of the above circumstances, and an object of the present invention is to improve the balance between tan δ (0°C) and tan δ (60°C) of a rubber composition.

The above object can be achieved by the present invention as described below. That is, the present invention relates to a rubber composition containing a diene rubber and a polymer filler containing at least a liquid crystal polymer and having an average particle size of 500 μm or less.

Liquid crystalline polymers exhibit unique dynamic viscoelasticity compared to diene rubbers, and have high heat loss over a wide temperature range. Therefore, when a polymer filler containing at least a liquid crystal polymer and having an average particle size of 500 μm or less is blended in addition to the diene rubber, the tan δ (0° C.) of the rubber composition is increased and the tan δ (60 °C) can be reduced. Furthermore, by designing the average particle size of the polymeric filler to be 500 μm or less, the dispersibility of the polymeric filler in the rubber component is improved. As a result, the balance between tan δ (0°C) and tan δ (60°C) of the rubber composition can be improved at a high level.

In the rubber composition, the liquid crystal polymer preferably has a transition temperature (Ti) from a liquid crystal phase to an isotropic phase of 20° C. or lower. Tan δ is represented by the ratio of loss modulus (E″) to storage modulus (E′) (tan δ=E″/E′). When a liquid crystal polymer having a Ti temperature of 20°C or less is blended into a rubber composition, it is relatively close to Ti at around 0°C and away from Ti at 60°C. tan δ greatly increases because E′ drops sharply compared to . On the other hand, since the liquid crystal polymer exists in the isotropic phase at around 60° C., both E″ and E′ gradually decrease, and the increase in tan δ is suppressed. As a result, the balance between tan δ (0°C) and tan δ (60°C) of the rubber composition can be improved to a higher level.

In the rubber composition, the liquid crystal polymer is preferably a liquid crystal elastomer. With such a configuration, the balance between tan δ (0° C.) and tan δ (60° C.) of the rubber composition can be improved to a higher level.

In the rubber composition, the liquid crystal polymer is preferably a liquid crystal polyurethane elastomer. The liquid crystalline polyurethane elastomer may be a reaction product of a mesogenic group-containing compound having at least an active hydrogen group and an isocyanate compound, and the liquid crystalline polyurethane elastomer contains at least a mesogenic group-containing compound having an active hydrogen group and an isocyanate compound. and a photopolymerizable group-containing compound. In these configurations, the liquid crystalline polyurethane elastomer exhibits high liquid crystallinity derived from the mesogenic group-containing compound and elasticity derived from the isocyanate compound. °C) can be improved to a higher level.

In the rubber composition, the liquid crystalline polyurethane elastomer is preferably an emulsion polymerized liquid crystalline polyurethane elastomer or a suspension polymerized liquid crystalline polyurethane elastomer. According to these configurations, the particle size of the polymer filler is uniformly controlled to a desired particle size. can be improved at higher levels.

In the above rubber composition, it is preferable that the blending amount of the polymer filler is 1 to 50 parts by mass when the total amount of the diene rubber is 100 parts by mass. In this case, the tan δ (0°C) of the rubber composition can be increased and the tan δ (60°C) can be decreased.

The present invention also relates to a pneumatic tire comprising any one of the rubber compositions described above. As described above, the rubber composition according to the present invention is designed to have a large tan δ (0°C) and a small tan δ (60°C). For this reason, a pneumatic tire comprising such a rubber composition, particularly a pneumatic tire using such a rubber composition for a tread member, improves both WET performance and fuel efficiency in a well-balanced manner.

A rubber composition according to the present invention contains a diene rubber and a polymer filler containing at least a liquid crystal polymer and having an average particle size of 500 μm or less.

Any rubber component that can be used as a raw material for pneumatic tires can be used as the rubber component, but diene rubber can be preferably used in the present invention. Diene rubbers include natural rubber (NR), polyisoprene rubber (IR), polystyrene butadiene rubber (SBR), polybutadiene rubber (BR), chloroprene rubber (CR), nitrile rubber (NBR) and the like. If necessary, those modified at the ends (eg, modified BR, modified SBR, etc.) or those modified to impart desired properties (eg, modified NR) can be preferably used. As for polybutadiene rubber (BR), in addition to those synthesized using cobalt (Co) catalyst, neodymium (Nd) catalyst, nickel (Ni) catalyst, titanium (Ti) catalyst, and lithium (Li) catalyst, WO2007 -129670 can also be used.

Considering the fuel efficiency of pneumatic tires, the polystyrene-butadiene rubber should have a styrene content of 10 to 40% by mass, a vinyl bond content in the butadiene portion of 10 to 70% by mass, and a cis content of 10% by mass or more. Particularly preferred are those having a styrene content of 15 to 25% by mass, a vinyl bond content in the butadiene portion of 10 to 60% by mass, and a cis content of 20% by mass or more. When the rubber composition according to the present invention is used as a tread rubber portion of a pneumatic tire, it is preferable to use a non-oil-added polystyrene-butadiene rubber rather than an oil-added type.

The polymer filler used in the present invention contains at least liquid crystal polymer and is designed to have an average particle size of 500 μm or less. The polymer filler may be composed only of liquid crystal polymer, or may be a mixture of liquid crystal polymer and various compounding agents that can be compounded with the rubber composition and processed into a filler shape. Various compounding agents that can be compounded in the rubber composition will be described later. Considering the dispersibility of the polymer filler in the diene rubber, the average particle size of the polymer filler is more preferably 300 μm or less, particularly preferably 100 μm or less. Although the lower limit of the average particle size of the polymeric filler is not particularly limited, it can be, for example, about 2 μm.

In the present invention, the average particle size of the polymer filler is the average particle size measured before blending in the rubber composition, and even if a plurality of polymer fillers aggregated during the compounding stage, the aggregation It shall mean the particle size previously measured. In the present invention, the polymer filler can be produced by various methods, and the method for measuring the average particle size of each polymer filler will be described later.

In the rubber composition according to the present invention, from the standpoint of improving the balance between tan δ (0°C) and tan δ (60°C) of the rubber composition, the total amount of the diene rubber is 100 parts by mass. , it is preferable to design to 1 to 50 parts by mass. If the amount of the polymeric filler compounded in the rubber composition is less than 1 part by mass, it becomes difficult to improve the WET performance and fuel efficiency of the pneumatic tire, which is the final product, in a well-balanced manner. exceeds 50 parts by mass, the physical properties of the rubber may be impaired. In order to improve WET performance and fuel economy in a well-balanced manner while maintaining the rubber physical properties of the pneumatic tire, which is the final product, when the total amount of the diene rubber is 100 parts by mass, the blending amount of the polymer filler is It is preferably 3 to 30 parts by mass, more preferably 5 to 20 parts by mass.

In the present invention, in order to improve the balance between tan δ (0 ° C.) and tan δ (60 ° C.) of the rubber composition at a higher level, the liquid crystal polymer has a transition temperature from the liquid crystal phase to the isotropic phase (Ti ) is preferably 20° C. or lower, and Ti is more preferably 5° C. or lower.

In the present invention, it is particularly preferred that the liquid crystal polymer is a liquid crystal elastomer. Liquid crystal elastomers include, for example, liquid crystal polyester elastomers, liquid crystal polyacrylate elastomers, liquid crystal polysiloxane elastomers, and liquid crystal polyurethane elastomers. Among these, the liquid crystalline polyurethane elastomer is particularly preferred because it can improve the balance between tan δ (0° C.) and tan δ (60° C.) to a higher level when compounded in a rubber composition.

Examples of the liquid crystalline polyurethane elastomer that can be used as a raw material for the polymer filler in the present invention include a reaction product of a mesogenic group-containing compound having at least an active hydrogen group, an isocyanate compound, and a photopolymerizable group-containing compound (hereinafter referred to as " Also referred to as "raw material reactant"). Each configuration will be described below.

As the mesogenic group-containing compound, for example, a compound represented by the following general formula (1) can be used.

In the above general formula (1), X is an active hydrogen group, R ₁ is a single bond forming part of the adjacent bonding group, -N=N-, -CO-, -CO-O-, or -CH =N—, R ₂ is a single bond forming part of the adjacent bonding group, or —O—, and R ₃ is a single bond forming part of the adjacent bonding group, or a It is an alkylene group. However, those in which R ₂ is —O— and R ₃ is a single bond forming part of the adjacent bonding group are excluded. ) In addition, the “single bond forming a part of the adjacent bonding group” means a state in which the single bond is shared with a part of the adjacent bonding group. For example, in the above general formula (1), when R ₁ is a single bond that forms part of the adjacent bonding group, the single bond R ₁ is shared with the benzene rings on both sides, and the benzene on both sides Forms a biphenyl structure with the ring. Examples of X include OH, SH, NH ₂ , COOH, secondary amine and the like. The compounding amount of the mesogenic group-containing compound is adjusted to 30 to 80% by mass, preferably 40 to 70% by mass, based on the total raw materials for the liquid crystalline polyurethane elastomer. When the compounding amount of the mesogenic group-containing compound is less than 30% by mass, it becomes difficult for the resulting polymer to exhibit liquid crystallinity. When the compounding amount of the mesogenic group-containing compound exceeds 80% by mass, the transition temperature (Ti) from the liquid crystal phase to the isotropic phase becomes high, making it difficult to mold the polymer at low temperatures including room temperature.

Alkylene oxide and/or styrene oxide are preferably used in combination with the mesogenic group-containing compound. Alkylene oxide and/or styrene oxide function to lower the temperature at which the liquid crystal phase appears in the liquid crystalline polyurethane elastomer. It becomes possible to easily design the transition temperature (Ti) from the liquid crystal phase to the isotropic phase within a desired temperature range. Alkylene oxides can be used, for example ethylene oxide, propylene oxide, or butylene oxide. The alkylene oxides listed above may be used alone or in combination of multiple types. Styrene oxide may have a substituent such as an alkyl group, an alkoxy group, or a halogen on the benzene ring. As the alkylene oxide, it is also possible to use a mixture of the above alkylene oxide and the above styrene oxide. The amount of alkylene oxide and/or styrene oxide is adjusted so that 4 to 20 mol, preferably 6 to 15 mol, of alkylene oxide and/or styrene oxide are added to 1 mol of the mesogenic group-containing compound.

As the isocyanate compound, for example, diisocyanate compounds shown below can be used. Examples of diisocyanate compounds include 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 2,2′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate, 4,4′-diphenylmethane diisocyanate, and 1,5-naphthalene diisocyanate. , p-phenylene diisocyanate, m-phenylene diisocyanate, p-xylylene diisocyanate, and m-xylylene diisocyanate; ethylene diisocyanate, 1,5-pentamethylene diisocyanate, 2,2,4-trimethylhexamethylene- Aliphatic diisocyanates such as 1,6-diisocyanate, 2,4,4-trimethylhexamethylene-1,6-diisocyanate, and 1,6-hexamethylene diisocyanate; and 1,4-cyclohexane diisocyanate, 4,4′-dicyclo alicyclic diisocyanates such as hexylmethane diisocyanate, isophorone diisocyanate, and norbornane diisocyanate; The exemplified diisocyanate compounds may be used singly or in combination of multiple types. In the present invention, a trifunctional or higher isocyanate compound may be used in combination as the isocyanate compound. When the total amount of the compounds is 100% by mass, the proportion of the diisocyanate compound is preferably 98% by mass or more, more preferably 99% by mass or more, and even more preferably about 100% by mass. Examples of tri- or more functional isocyanate compounds include triphenylmethane triisocyanate, tris(isocyanatophenyl)thiophosphate, lysine ester triisocyanate, 1,3,6-hexamethylene triisocyanate, 1,6,11-undecane triisocyanate, Triisocyanates such as 1,8-diisocyanato-4-isocyanatomethyloctane, bicycloheptane triisocyanate, and tetraisocyanates such as tetraisocyanatosilane.

The ratio of the isocyanate compound is preferably 10 to 40 parts by mass, more preferably 15 to 30 parts by mass, when the total amount of the mesogenic group-containing compounds constituting the liquid crystalline polyurethane elastomer is 100 parts by mass. If the amount of the isocyanate compound is less than 10 parts by mass, polymerization by urethane reaction will be insufficient. On the other hand, when the ratio of the isocyanate compound exceeds 40 parts by mass, the amount of the mesogenic group-containing compound in the total raw material of the liquid crystalline polyurethane elastomer is relatively small, resulting in deterioration of the liquid crystalline property of the liquid crystalline polyurethane elastomer.

The isocyanate group of the isocyanate compound can react with an active hydrogen group such as a hydroxyl group of the mesogenic group-containing compound and an active hydrogen group such as a hydroxyl group of the photopolymerizable group-containing compound. NCO INDEX (NCO/OH), which is the theoretical amount of isocyanate groups in the isocyanate compound with respect to the theoretical amount of active hydrogen groups in the mesogenic group-containing compound and the photopolymerizable group-containing compound, is 0.70 to 1.10. is preferred, and 0.80 to 0.95 is more preferred. In the present invention, particularly when the liquid crystal filler is composed of an emulsion polymerized liquid crystal polyurethane elastomer or a suspension polymerized liquid crystal polyurethane elastomer, it is preferable to design the NCO INDEX within such a range because the molecular weight of the elastomer can be reduced.

Examples of photopolymerizable group-containing compounds that can be used include acryloyl group-containing compounds, methacryloyl group-containing compounds, and allyl compounds. Examples of acryloyl group-containing compounds include propylene glycol diglycidyl ether acrylic acid adduct, ethylene glycol diglycidyl ether methacrylic acid adduct, tripropylene glycol diglycidyl ether acrylic acid adduct, glycerin diglycidyl ether acrylic acid adduct, and bisphenol A. PO2mol adduct diglycidyl ether acrylic acid adduct, 2-acryloyloxyethyl succinate, β-carboxyethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 2-hydroxy-3-phenoxy Propyl acrylate, 2-acryloyloxyethyl-succinic acid, 2-acryloyloxyethylhexahydrophthalate, 2-acryloyloxyethyl-phthalate, 2-acryloyloxyethyl-2-hydroxyethyl-phthalate, 2 -acryloyloxyethyl acid phosphate, 2-hydroxy-3-acryloyloxypropyl methacrylate, pentaerythritol triacrylate and the like. Examples of methacryloyl group-containing compounds include 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 2-methacryloyloxyethyl succinate, 2-methacryloyloxyethylhexahydrophthalate, and 2-methacryloyl. oxyethyl acid phosphate, glycerin dimethacrylate, bisphenol A PO2mol adduct diglycidyl ether methacrylic acid adduct, bisphenol A diglycidyl ether methacrylic acid adduct, 2-hydroxy-3-acryloyloxypropyl methacrylate, 2-methacryloyloxyethyl succinate nate and the like. Examples of allyl group-containing compounds include glycerin monoallyl ether, trimethylolpropane diallyl ether, pentaerythritol triallyl ether, and the like.

When the total amount of the mesogenic group-containing compounds constituting the liquid crystalline polyurethane elastomer is 100 parts by mass, the proportion of the photopolymerizable group-containing compound is preferably 1 to 12 parts by mass, more preferably 5 to 10 parts by mass. preferable. If the ratio of the photopolymerizable group-containing compound is outside the above-described range, the balance between tan δ (0°C) and tan δ (60°C) may not be sufficiently improved when blended in the rubber composition.

In addition to the mesogenic group-containing compound having an active hydrogen group, the isocyanate compound, and the photopolymerizable group-containing compound, an active hydrogen group-containing compound may be used as a raw material for the liquid crystalline polyurethane elastomer. Active hydrogen group-containing compounds include, for example, polyol compounds and amine compounds. Polyol compounds include, for example, polyether polyol, polyester polyol, polycarbonate polyol, polyester polycarbonate polyol, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butane Diol, 1,4-butanediol, 2,3-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, 1,4-bis(2-hydroxyethoxy)benzene, trimethylolpropane, glycerin, 1,2,6-hexanetriol, meso-erythritol, pentaerythritol, tetramethylolcyclohexane, methylglucoside, sorbitol, mannitol, dulcitol, sucrose, 2,2,6,6-tetrakis(hydroxymethyl)cyclohexanol, diethanolamine, N-methyldiethanolamine, triethanolamine, and the like. Amine compounds include ethylenediamine, tolylenediamine, diphenylmethanediamine, diethylenetriamine, monoethanolamine, 2-(2-aminoethylamino)ethanol, monopropanolamine, and the like. Each active hydrogen group-containing compound listed above may be used alone, or a plurality of types may be mixed and used.

Further, when reacting a mesogenic group-containing compound having an active hydrogen group, an isocyanate compound, and a photopolymerizable group-containing compound, a urethane polymerization catalyst known to those skilled in the art may be used. Such polymerization catalysts include organic tin catalysts such as dibutyltin dilaurate and tin octylate, triethylenediamine and its derivatives, N-methylmorpholine, N,N,N',N'-tetramethylethylenediamine, N,N,N ',N'-tetramethylhexamethylenediamine, 1,8-diazabicyclo[5,4,0]undecene-7 (DBU), bis(N,N-dimethylamino-2-ethyl) ether, bis(2-dimethyl tertiary amine-based catalysts such as aminoethyl)ether; carboxylic acid metal salt catalysts such as potassium acetate and potassium octylate; and imidazole-based catalysts. Among these, the use of triethylenediamine and its derivatives is preferred.

As the production conditions for producing the raw material reactant, at least three of the mesogenic group-containing compound having an active hydrogen group, the isocyanate compound, and the photopolymerizable group-containing compound are heated to, for example, 60 to 150 ° C. A method of reacting the three components while heating and melting may be used.

In the present invention, the liquid crystalline polyurethane elastomer is preferably an emulsion polymerized liquid crystalline polyurethane elastomer or a suspension polymerized liquid crystalline polyurethane elastomer from the viewpoint of controlling the particle size of the polymeric filler to be uniform and desired. As an example, an emulsion-polymerized liquid crystal polyurethane elastomer will be described below.

The emulsion-polymerized liquid crystal polyurethane elastomer can be produced, for example, by emulsion-polymerizing raw reactants in water in the presence of a surfactant. When used as a raw material for an emulsion-polymerized liquid crystal polyurethane elastomer, the molecular weight of the starting reactant is preferably not so large, for example, a weight-average molecular weight of about 1,000 to 20,000 is preferred.

As the surfactant, those commonly used in emulsion polymerization can be used, and any of anionic, nonionic and cationic surfactants can be used. The amount of surfactant used in emulsion polymerization can be arbitrarily designed in order to adjust the average particle size of the polymer filler to be produced within the desired range. 0.01 to 5% by mass.

A polymerization initiator may be used when emulsifying the raw reactant in water in the presence of a surfactant. Both a photopolymerization initiator and a thermal polymerization initiator can be used as the polymerization initiator. When using a photopolymerization initiator, from the viewpoint of productivity and uniform dispersion of the photopolymerization initiator, when producing the raw material reactant, in the presence of the photopolymerization initiator, a mesogenic group-containing compound having at least an active hydrogen group , an isocyanate compound and a photopolymerizable group-containing compound are reacted to produce a raw material reaction product containing a photopolymerization initiator, which is subjected to light of a wavelength of 200 to 600 nm in water in the presence of a surfactant. Irradiation may produce polymeric fillers of desired average particle size.

Photoinitiators are, for example, 1-hydroxy-cyclohexyl-phenyl-ketone, bis(2,4,6-trimethylbenzoyl)-phenylphosphone oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 2,2-dimethoxy-1,2-diphenylethan-1-one, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-hydroxy-cyclohexyl-phenyl-ketone/benzophenone, 1-[ 4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl )-benzyl]-phenyl}-2-methyl-propan-1-one, oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester/oxy-phenyl-acetic Acid 2-[2-hydroxy-ethoxy]-ethyl ester, phenylglyoxylic acid methyl ester, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl -2-dimethylamino-1-(4-morpholinophenyl)-butanone-1,2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butane -1-one, bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium, 1,2-octane dione, 1-[4-(phenylthio)phenyl-,2-(O-benzoyloxime)], ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]- , 1-(O-acetyloxime), iodonium, (4-methylphenyl)[4-(2-methylpropyl)phenyl]-hexafluorophosphate (1-)/propylene carbonate, triarylsulfonium hexafluorophosphate , triarylsulfonium tetrakis-(pentafluorophenyl)borate, and oximesulfonate-based photoacid generators can be used. The ratio of the photopolymerization initiator is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 8 parts by mass when the total amount of the mesogenic group-containing compound constituting the raw material reactant is 100 parts by mass. is more preferable. If the amount of the photopolymerization initiator is less than 0.1 parts by mass, the polymerization reaction may not proceed uniformly during light irradiation, or curing may be insufficient. When the amount of the photoreaction initiator is more than 10 parts by mass, the content of mesogenic groups in the produced elastomer decreases, which may make it difficult to develop a liquid crystal phase. The photoinitiator preferably has an absorption wavelength of 200 to 600 nm. As long as the photoinitiator has an absorption wavelength within the above range, the photoinitiator absorbs light even if the liquid crystal polyurethane elastomer or its raw material has low transparency (visible light transmittance), The photocrosslinking reaction can be reliably advanced.

The average particle size of the polymer filler containing at least the emulsion-polymerized liquid-crystalline polyurethane elastomer can be measured, for example, by laser diffractometry of the emulsion-polymerized liquid-crystalline polyurethane elastomer dispersed in water after emulsion polymerization. A laser diffraction method can measure a particle size of about 0.03 to 1000 μm. Moreover, when the average particle size of the resulting emulsion-polymerized liquid crystal polyurethane elastomer is small, it can also be measured by a dynamic light scattering method (DLS). DLS can measure a particle size of about 0.0014 to 7 μm. When the emulsion polymerized liquid crystalline polyurethane elastomer is used as a raw material in the present invention, the average particle size measured by the laser diffraction method or DLS can be regarded as the average particle size measured before blending in the rubber composition.

When a thermal polymerization initiator is used for emulsion polymerization of raw reactants in water in the presence of a surfactant, it can be emulsified in water or premixed with the raw reactants. Thermal polymerization initiators known to those skilled in the art can be used.

Suspension-polymerized liquid crystal polyurethane elastomer can be produced by suspension-polymerizing raw reactants and water while mechanically stirring. Surfactants and/or polymerization initiators can be used as necessary during suspension polymerization, and examples of these include those that can be used in emulsion polymerization. The average particle size of the polymer filler containing at least the suspension polymerized liquid crystal polyurethane elastomer can also be determined by the same method as for the emulsion polymerized liquid crystal polyurethane elastomer.

In the present invention, the liquid crystalline polyurethane elastomer may be composed of a reaction product of at least a mesogenic group-containing compound having an active hydrogen group and an isocyanate compound. In this case, a liquid crystalline polyurethane elastomer may be produced by reacting a mesogenic group-containing compound having an active hydrogen group, an isocyanate compound, and a tri- or higher functional polyol component in order to introduce a cross-linking component. . The liquid crystalline polyurethane elastomer thus produced can be made into polymer filler by granulating it by a method such as cryo-pulverization.

In addition to the rubber component and the polymer filler, the rubber composition according to the present invention contains carbon black, silica, a silane coupling agent, an anti-aging agent, a softening agent such as zinc oxide, stearic acid, wax and oil, and Various compounding agents such as processing aids can be included.

Examples of carbon black include carbon blacks commonly used in the rubber industry such as SAF, ISAF, HAF, FEF and GPF, as well as conductive carbon blacks such as acetylene black and ketjen black.

As silica, wet-process silica and dry-process silica can be used, but it is particularly preferable to use wet-process silica containing hydrous silicic acid as a main component.

As the silane coupling agent, a silane coupling agent having reactivity with diene rubber is used. Silane coupling agents that can be used in the present invention include, for example, bis(3-triethoxysilylpropyl) tetrasulfide (eg, "Si69" manufactured by Degussa), bis(3-triethoxysilylpropyl) disulfide (eg, Degussa "Si75"), bis (2-triethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) disulfide, bis (3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilyl) sulfide silanes such as ethyl)disulfide; Protected mercaptosilanes such as 1-propyltriethoxysilane, 3-propionylthiopropyltrimethoxysilane and the like.

Antiaging agents include aromatic amine antiaging agents, amine-ketone antiaging agents, monophenol antiaging agents, bisphenol antiaging agents, polyphenol antiaging agents, and dithiocarbamic acid, which are commonly used for rubber. Antiaging agents such as salt-based anti-aging agents and thiourea-based anti-aging agents may be used singly or in an appropriate mixture.

After the step of mixing compounding agents other than the vulcanization compounding agent, the vulcanization compounding agent is further mixed and dispersed. Examples of vulcanization compounding agents used in the step of mixing vulcanization compounding agents include vulcanizing agents such as sulfur and organic peroxides, vulcanization accelerators, vulcanization accelerator auxiliaries, and vulcanization retarders. be done.

Sulfur as a sulfur-based vulcanizing agent may be ordinary sulfur for rubber, such as powdered sulfur, precipitated sulfur, insoluble sulfur, highly dispersible sulfur, and the like.

As vulcanization accelerators, sulfenamide-based vulcanization accelerators, thiuram-based vulcanization accelerators, thiazole-based vulcanization accelerators, thiourea-based vulcanization accelerators, and guanidine-based vulcanization accelerators, which are commonly used for rubber vulcanization. Vulcanization accelerators such as accelerators and dithiocarbamate-based vulcanization accelerators may be used singly or in an appropriate mixture.

The rubber composition according to the present invention comprises a rubber component and a polymer filler, and optionally carbon black, silica, a silane coupling agent, a vulcanization compounding agent, an antioxidant, zinc oxide, stearic acid, wax, and oil. It can be obtained by kneading a softening agent, a processing aid, and the like, using a kneader commonly used in the rubber industry, such as a Banbury mixer, a kneader, and a roll.

In addition, the method of blending each of the above components is not particularly limited, and blending components other than vulcanization compounding agents such as sulfur vulcanizing agents and vulcanization accelerators are kneaded in advance to form a masterbatch, and the remaining components are added. A method of adding each component in an arbitrary order and kneading, a method of adding all the components at the same time and kneading, and the like may be used.

Examples and the like that specifically show the configuration and effects of the present invention will be described below. The evaluation items in Examples and the like were measured as follows.

<Transition temperature (Ti)>
A differential scanning calorimeter [DSC] (product name: X-DSC 7000, manufactured by Hitachi High-Tech Science Co., Ltd.) was used to measure the transition temperature (Ti) of raw reactants 1 to 3 and polymer fillers 1 to 7.

<Average Particle Diameter of Polymer Filler (Emulsion Polymerized Liquid Crystal Polyurethane Elastomer)>
The average particle size of the polymer filler containing the emulsion polymerized liquid crystal polyurethane elastomer is determined by measuring the average particle size of the emulsion polymerized liquid crystal polyurethane elastomer dispersed in water with a laser diffraction particle size distribution analyzer (product name: SALD -2200", manufactured by Shimadzu Corporation), and measured by a laser diffraction method.

<Dynamic viscoelasticity measurement>
The rubber compositions of Examples 1 to 8 and the rubber composition of Comparative Example 1 were vulcanized by heating at 160° C. for 20 minutes, molded into predetermined shapes, and used as measurement samples. For each measurement sample, a dynamic viscoelasticity measuring device (product name "Fully automatic viscoelasticity analyzer VR-7110", manufactured by Ueshima Seisakusho Co., Ltd.) was used to measure the storage elastic modulus (E') and the loss elastic modulus (E"), tan δ (0° C.) and tan δ (60° C.) were obtained, and Table 3 shows the tan δ value of Comparative Example 1 as 100. The measurement conditions are as follows.
Size of measurement sample: length 40 mm, width 3 mm, thickness 2 mm
Measurement mode: Tensile mode Measurement temperature: 0°C, 60°C
Frequency: 100Hz
Dynamic strain: 0.15%

<Hardness measurement>
The rubber compositions of Examples 1 to 8 and the rubber composition of Comparative Example 1 were vulcanized by heating at 160° C. for 20 minutes, molded into predetermined shapes, and used as measurement samples. For each measurement sample obtained, the hardness at 23° C. (according to JIS K6253) was measured with a durometer type A (model: GS-719N, manufactured by Teclock Co., Ltd.). In Table 3, the hardness value of Comparative Example 1 is represented by an index of 100.

(Production of mesogendiol A)
In a reaction vessel, BH6 (500 g) as a mesogenic group-containing compound having an active hydrogen group, potassium hydroxide (19 g), and N,N-dimethylformamide (3000 ml) as a solvent are added and mixed, and further, propylene as an alkylene oxide 8.8 equivalents of oxide were added to 1 mol of BH6, and the mixture was reacted at 120° C. for 2 hours under pressure (addition reaction). Then, oxalic acid (15 g) was added to the reaction vessel to stop the addition reaction, insoluble salts in the reaction solution were removed by suction filtration, and N,N-dimethylformamide in the reaction solution was removed by distillation under reduced pressure. Mesogendiol A was obtained by removing by Mesogendiol A has a hydroxyl value of 141. A synthesis scheme of mesogendiol A is shown in formula (2). Mesogendiol A shown in formula (2) is a representative one and may include various structural isomers. n ^* in formula (2) is an average of 4.4.

(Production of mesogendiol B)
In a reaction vessel, BHBA6 (500 g) as a mesogenic group-containing compound having an active hydrogen group, potassium hydroxide (19 g), and N,N-dimethylformamide (3000 ml) as a solvent are added and mixed, and further, propylene as an alkylene oxide. 8.4 equivalents of oxide were added to 1 mol of BHBA6, and the mixture was reacted under pressure at 120°C for 2 hours (addition reaction). Then, oxalic acid (15 g) was added to the reaction vessel to stop the addition reaction, insoluble salts in the reaction solution were removed by suction filtration, and N,N-dimethylformamide in the reaction solution was removed by distillation under reduced pressure. Mesogen diol B was obtained by removing by The hydroxyl value of mesogen diol B is 137. A synthesis scheme of mesogendiol B is shown in Formula (3). Note that the mesogen diol B shown in formula (3) is a representative one and may include various structural isomers. n ^* in formula (3) is an average of 4.2.

(Production of raw material reactants 1 to 3)
With respect to 100 parts by mass of mesogen diol A or mesogen diol B, 1,6-hexamethylene diisocyanate (manufactured by Tokyo Chemical Industry Co., Ltd.) as an isocyanate compound, 2-hydroxyethyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd.) as a photopolymerizable group-containing compound, 2,4,6-Trimethylbenzoyl-diphenyl-phosphine oxide (TPO) (manufactured by IGM resins) was blended as a photoreaction initiator at the compounding ratio shown in Table 1, and these were mixed at 80°C while stirring. , to produce raw reactants 1-3.

(Production of polymer fillers 1 to 7)
Raw material reactants 1 to 3, each surfactant, and water are blended in a predetermined ratio, and a tabletop UV curing device (product name: eye mini grantage (ESC-1511U), manufactured by eye graphics) is used to cure at a wavelength of 200. Polymer fillers 1 to 7 containing emulsion polymerized liquid crystalline polyurethane elastomer were produced by irradiation with light of ~600 nm (irradiation energy 800 mJ). After emulsion polymerization, the average particle size of the emulsion polymerized liquid crystalline polyurethane elastomer dispersed in water was measured by the above method, dried at 110°C for 10 hours, and further vacuum dried at 110°C. .

(Production of rubber compositions of Examples 1 to 8 and Comparative Example 1)
Polymer fillers 1 to 7 thus obtained were blended with a diene rubber (SBR, trade name: SL563, manufactured by JSR) using a lab mixer (product name: Laboplastomill, manufactured by Toyo Seiki Seisakusho). The compounding procedure is the compounding ratio shown in Table 3, and as the first step, silica (trade name: Nip Seal AQ, manufactured by Tosoh Silica Co., Ltd.), a silane coupling agent (bis(3-triethoxysilyl Propyl) tetrasulfide, trade name: Si69, manufactured by Evonik Deguza), zinc white (trade name: type 1 zinc white, manufactured by Mitsui Mining & Smelting Co., Ltd.), stearic acid (trade name: Lunax S-20, manufactured by Kao Corporation) ), and an anti-aging agent (trade name: Nocrac 6C, manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.) are added and kneaded at 160 ° C. Then, in the second step, a polymer filler is added to the kneaded product to make it 160 ° C., and in the third step, the kneaded product is added with sulfur (rubber powder sulfur 150 mesh, manufactured by Hosoi Chemical Industry Co., Ltd.) and a vulcanization accelerator (trade name: Noxeller CZ (primary vulcanization accelerator) , Noccellar D (secondary vulcanization accelerator), both manufactured by Ouchi Shinko Kagaku Kogyo Co., Ltd.) were added and kneaded at 90 ° C., and the obtained rubber compositions of Examples 1 to 8 and Comparative Example 1 and

From the results in Table 3, the vulcanized rubbers of the rubber compositions of Examples 1 to 8 maintained their hardness and had a large increase in tan δ (0°C), but an increase in tan δ (60°C) It can be seen that the balance between tan δ (0° C.) and tan δ (60° C.) is improved.

Claims (5)

A rubber composition containing a diene rubber and a polymer filler,
The polymer filler is a particulate polymer filler containing at least a liquid crystal polymer and having an average particle size of 500 μm or less,
The liquid crystal polymer is a liquid crystal elastomer having a transition temperature (Ti) from a liquid crystal phase to an isotropic phase of 20° C. or less,
The liquid crystal polymer is a liquid crystal polyurethane elastomer,
A rubber composition , wherein the liquid crystalline polyurethane elastomer is an emulsion polymerized liquid crystalline polyurethane elastomer . 2. The rubber composition according to claim 1 , wherein said liquid crystal polyurethane elastomer is a reaction product of a mesogenic group-containing compound having at least an active hydrogen group and an isocyanate compound. 2. The rubber composition according to claim 1 , wherein said liquid crystal polyurethane elastomer is a reaction product of a mesogenic group-containing compound having at least an active hydrogen group, an isocyanate compound, and a photopolymerizable group-containing compound. The rubber composition according to any one of claims 1 to 3 , wherein the amount of the polymer filler compounded is 1 to 50 parts by mass when the total amount of the diene rubber is 100 parts by mass. A pneumatic tire comprising the rubber composition according to any one of claims 1 to 4 .