JP7261652B2 - 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 vulcanized rubber obtained may deteriorate, so a technique for improving these in a well-balanced manner has been desired. .

In Patent Document 1 below, by using, as a rubber component, a rubber composition containing at least two diene-based rubbers having a bimodal temperature distribution curve of tan δ, WET performance and fuel efficiency of a pneumatic tire are improved. 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 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 liquid crystal elastomer.

Liquid crystalline elastomers exhibit unique dynamic viscoelasticity compared to diene rubbers, and have high heat loss over a wide temperature range. Therefore, when a liquid crystal elastomer is compounded in addition to the diene rubber, the tan δ (0°C) of the rubber composition can be increased and the tan δ (60°C) can be decreased.

In the above rubber composition, the liquid crystal elastomer preferably has a transition temperature (Ti) from a liquid crystal phase to an isotropic phase of 20° C. or less. Tan δ is represented by the ratio of loss modulus (E″) to storage modulus (E′) (tan δ=E″/E′). When a liquid crystalline elastomer 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. Therefore, E″ near 0° C. In comparison, E' sharply decreases, so tan δ greatly increases. On the other hand, since the liquid crystalline elastomer exists in the isotropic phase at around 60° C., both E″ and E′ gradually decrease, thereby suppressing an increase in tan δ. 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 elastomer preferably has a functional group that reacts with the diene rubber. According to such a configuration, the dispersibility of the liquid crystal elastomer in the diene rubber is improved, and the balance between tan δ (0° C.) and tan δ (60° C.) of the rubber composition is further improved, and finally obtained The physical properties of the vulcanized rubber are also improved. In the rubber composition, the functional group is more preferably a functional group containing at least a sulfur atom.

In the rubber composition, the liquid crystal elastomer 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, an isocyanate compound, a polysulfide-containing compound, and a photopolymerizable group-containing compound, and a mesogen having at least an active hydrogen group. A reaction product of a group-containing compound, an isocyanate compound, a polysulfide-containing compound, and a polyfunctional compound may also be used. 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. Furthermore, in these configurations, since the liquid crystalline polyurethane elastomer has a polysulfide structure in the molecule, when the rubber composition is mixed and the rubber composition is vulcanized, the liquid crystalline polyurethane elastomer reacts with the rubber component via the polysulfide structure. do. As a result, since the liquid crystalline polyurethane elastomer is highly dispersed in the rubber component, 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 amount of the liquid crystal elastomer is preferably 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). Therefore, 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 liquid crystal elastomer.

As the rubber component, any rubber component that can be used as a raw material for pneumatic tires can be used arbitrarily. In the present invention, diene rubber can be preferably used. 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.

In the present invention, 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 blended in a rubber composition.

Considering the dispersibility in the diene rubber, the average particle size of the liquid crystal elastomer used in the present invention is preferably designed to be 500 μm or less. Considering the dispersibility of the liquid crystal elastomer in the diene rubber, the average particle size of the liquid crystal elastomer is more preferably 300 μm or less, particularly preferably 100 μm or less. Although the lower limit of the average particle size of the liquid crystal elastomer is not particularly limited, it can be, for example, about 2 μm.

In the rubber composition according to the present invention, the compounding amount of the liquid crystalline elastomer is 100 parts by mass based on the total amount of the diene rubber from the standpoint of improving the balance between tan δ (0°C) and tan δ (60°C) of the rubber composition. When, it is preferable to design to 1 to 50 parts by mass. If the amount of the liquid crystal elastomer 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. If it exceeds 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, the compounding amount of the liquid crystal elastomer is 3 when the total amount of the diene rubber is 100 parts by mass. It is preferably up to 50 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 crystalline elastomer has a transition temperature (Ti) is preferably 20° C. or lower, and Ti is more preferably 5° C. or lower.

In the present invention, the liquid crystal elastomer preferably has a functional group that reacts with the diene rubber, and more preferably the functional group contains at least a sulfur atom. Liquid crystal elastomers having functional groups containing at least a sulfur atom include, for example, liquid crystal polyurethane elastomers which are reaction products of polysulfide-containing compounds, which will be described later.

Examples of the liquid crystalline polyurethane elastomer that can be used in the present invention include (i) a reaction product of a mesogenic group-containing compound having at least an active hydrogen group, an isocyanate compound, a polysulfide-containing compound, and a photopolymerizable group-containing compound. (ii) a reaction product of a mesogenic group-containing compound having at least an active hydrogen group, an isocyanate compound, a polysulfide-containing compound, and a polyfunctional compound. Both (i) and (ii) above correspond to liquid crystalline polyurethane elastomers which are reactants of polysulfide-containing compounds. Each configuration will be described below.

As the mesogenic group-containing compound used in (i) and (ii) above, 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 used in (i) and (ii) above, 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, and the like. 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 possessed by the isocyanate compound includes active hydrogen groups such as hydroxyl groups possessed by mesogenic group-containing compounds, active hydroxyl groups such as hydroxyl groups possessed by polysulfide-containing compounds, and active hydrogen groups such as hydroxyl groups possessed by photopolymerizable group-containing compounds. can react. NCO INDEX (NCO/OH), which is the theoretical amount of isocyanate groups possessed by the isocyanate compound with respect to the theoretical amount of active hydrogen groups possessed by the mesogenic group-containing compound, the polysulfide-containing compound and the photopolymerizable group-containing compound, is 0.70-1. It is preferably 10, more preferably 0.8 to 0.95. In the present invention, particularly when the liquid crystal elastomer 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 the polysulfide-containing compound used in (i) and (ii) above include compounds containing an active hydroxyl group such as a hydroxyl group and a polysulfide group. Specifically, for example, bis(2-hydroxyethyl)disulfide, dithiodiglycolic acid, 3,3-dithiodipropionic acid, 4,4-dithionibutyric acid, 2,2-dithiodipropionic acid, bis(4- hydroxyphenyl)disulfide, bis(6-hydroxy-2-naphthyl)disulfide, 2,2-dithiodibenzoic acid, 6,6-dithiodinicotinic acid, 5,5-dithiobis(2-nitrobenzoic acid), 2, 2-dithiodianiline, 4,4-dithiodianiline (R)-α-lipoic acid, xanthan hydride, 3-(2-pyridyldithio)propionic acid, cystamine dihydrochloride, formamidine disulfide dihydrochloride, cystine ( DL-, meso-mixture), L-(-)-cystine, L-(-)-cystine dihydrochloride, L-cystine dimethyl dihydrochloride, DL-homocystine, bis[2-(4-azidosalicylamide) ethyl]disulfide, 2,2'-dithiobis(6-fluorobenzoic acid), lipoamide-PEG12-carboxylic acid, bis(2-benzamidophenyl)disulfide, N,N'-dicarbobenzoxy-L-cystine, pyritinol, etc. is mentioned.

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 polysulfide-containing compound is preferably 0.01 to 30 parts by mass, more preferably 0.01 to 20 parts by mass. more preferred. If the amount of the polysulfide-containing compound is less than 0.01 parts by mass, the dispersibility of the liquid crystalline polyurethane elastomer in the rubber composition deteriorates, and the rubber physical properties of the rubber composition, tan δ (0° C.) and tan δ (60 °C) may not be improved. On the other hand, when the ratio of the polysulfide-containing compound exceeds 30 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 liquid crystallinity of the liquid crystalline polyurethane elastomer.

Examples of the photopolymerizable group-containing compound used in (i) above 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, the polysulfide-containing compound, and the photopolymerizable group-containing compound used in (i) and (ii) above, active hydrogen is used as a raw material for the liquid crystalline polyurethane elastomer. Group-containing compounds may also be used. 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 the mesogenic group-containing compound having an active hydrogen group used in (i) and (ii), the isocyanate compound, the polysulfide-containing compound, and the photopolymerizable group-containing compound, known to those skilled in the art A urethane polymerization catalyst may also 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.

In the above (i), the production conditions for producing the raw material reactant include a mesogenic group-containing compound having at least an active hydrogen group, an isocyanate compound, a polysulfide-containing compound, and a photopolymerizable group-containing compound. is heated to, for example, 60 to 150° C., and the four components are reacted while being heated and melted.

In (i) above, 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 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 is, for example, a reaction product (hereinafter also referred to as a "raw material reactant") of a mesogenic group-containing compound having at least an active hydrogen group, an isocyanate compound, a polysulfide-containing compound, and a photopolymerizable group-containing compound. ) can be produced by emulsion polymerization 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 to adjust the average particle size of the liquid crystal elastomer to be produced within a desired range. It may be designed to be 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, a polysulfide-containing compound, and a photopolymerizable group-containing compound are reacted to produce a photopolymerizable initiator-containing raw material reaction product, which is then dissolved in water in the presence of a surfactant at a wavelength of By irradiating with light of 200 to 600 nm, an emulsion polymerized liquid crystalline polyurethane elastomer having a desired average particle size may be produced.

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, 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 emulsion-polymerized liquid-crystal polyurethane elastomer can be measured, for example, by a laser diffraction method after the emulsion-polymerized liquid-crystal polyurethane elastomer is dispersed in water. 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 suspension polymerized liquid crystal polyurethane elastomer can also be determined by the same method as for the emulsion polymerized liquid crystal polyurethane elastomer.

Examples of the polyfunctional compound used in (ii) above include compounds having three or more functional groups capable of reacting with an active hydrogen group or an isocyanate group. Specific examples include triols such as glycerin and trimethylolpropane; tetraols such as pentaerythritol; diamines such as 4′-diaminodiphenylmethane (MOCA); aminoalcohols such as diethanolamine, triethanolamine and aminoethylethanolamine;

In addition to the rubber component and the liquid crystal elastomer, 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 a processing agent. Various compounding agents such as auxiliary agents can be blended.

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 combination as appropriate.

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 liquid crystal elastomer, and optionally carbon black, silica, a silane coupling agent, a vulcanization compounding agent, an antioxidant, zinc oxide, stearic acid, wax, oil, and the like. The softening agent, processing aid, etc. are kneaded 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. Compounding components other than vulcanization compounding agents such as sulfur-based 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.

In the present invention, after mixing the diene rubber and the liquid crystalline elastomer, preferably after mixing the diene rubber and the liquid crystalline elastomer having a functional group that reacts with the diene rubber, more preferably the diene rubber and the liquid crystalline elastomer are mixed. A vulcanized rubber in which a liquid crystalline elastomer is dispersed in a diene rubber by mixing with a liquid crystalline polyurethane elastomer which is a reaction product of a polysulfide-containing compound that reacts with a diene rubber, and then vulcanizing the obtained rubber composition. can be manufactured. Since the vulcanized rubber has a structure in which the diene rubber and the liquid crystal elastomer are chemically reacted, the tan δ (0° C.) and the tan δ (60° C.) are well balanced, and the rubber physical properties are also excellent. Therefore, it is particularly useful, for example, as a tread member for pneumatic tires.

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)>
The transition temperature (Ti) of raw reactants 1 to 6 and liquid crystal polyurethane fillers 1 to 8 was measured using a differential scanning calorimeter [DSC] (product name: X-DSC 7000, manufactured by Hitachi High-Tech Science).

<Average particle size of liquid crystal polyurethane fillers 1 and 2>
The particle size after freeze pulverization was calculated by image analysis (accelerating voltage: 15 kV) with a scanning electron microscope (product name: SU3500, manufactured by Hitachi High-Technologies Corporation).

<Average particle size of liquid crystal polyurethane fillers 3 to 8>
The average particle size of the liquid crystal polyurethane fillers 3 to 8 (emulsion polymerized liquid crystal polyurethane elastomer) was determined by measuring the average particle size of the emulsion polymerized liquid crystal polyurethane elastomer dispersed in water after emulsion polymerization using a laser diffraction particle size distribution analyzer (product name It was measured by a laser diffraction method using "SALD-2200" manufactured by Shimadzu Corporation).

<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 determined, and are shown in Table 3 as indices with the tan δ value of Comparative Example 1 set to 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%

<Breaking elongation and breaking strength 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, and dumbbell-shaped No. 3 test pieces with a thickness of 2 mm conforming to JIS K 6251. It was molded into a sample for measurement. Using a tensile tester (manufactured by Shimadzu Corporation, precision universal testing machine Autograph AG-X), the strength at break and the elongation at break were measured for each measurement sample obtained. Table 3 shows the measured values.

(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 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. 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 4.4 on average.

(Production of raw material reactants 1 to 6)
For 100 parts by mass of mesogen diol A, 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, and a photoreaction initiator 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (TPO) (manufactured by IGM resins) as a polysulfide-containing compound, 3,3-dithiodipropionic acid (manufactured by Tokyo Chemical Industry Co., Ltd.), bis(2-hydroxy Ethyl)disulfide (manufactured by Tokyo Chemical Industry Co., Ltd.) or 4,4-dithiodianiline (manufactured by Tokyo Chemical Industry Co., Ltd.) is blended at the blending ratio shown in Table 1, and these are mixed at 80 ° C. while stirring to obtain raw materials. Reactions 1-6 were prepared.

(Production of liquid crystal polyurethane fillers 1 and 2)
After blending at the compounding ratio shown in Table 1 and mixing at 80 ° C. with stirring, the resulting reaction product was cooled with liquid nitrogen, and then a pulverizer (rotor speed mill P-14 manufactured by Fritsch) was used. Liquid crystalline polyurethane fillers 1 and 2 were produced by freeze pulverizing under the following conditions.
Rotor speed [rpm] 15000
Sieve ring hole size [mm] 0.5
Impact rotor blade number [sheet] 12

(Production of liquid crystal polyurethane fillers 3 to 8)
Raw material reactants 1 to 6, 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. Liquid crystalline polyurethane fillers 3 to 8 (emulsion polymerized liquid crystalline polyurethane elastomers) 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)
The obtained liquid crystal polyurethane fillers 1 to 8 were blended with a diene rubber (SBR, trade name: SL563, manufactured by JSR Corporation) 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 Degusa), 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. ° 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: Noccellar 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. to obtain rubber compositions of Examples 1 to 8. In the remarks of Table 3, "pulverization" indicates that the liquid crystal polyurethane filler is "frozen pulverized product", "emulsification" indicates that the liquid crystal polyurethane filler is "emulsion polymerized product", for example, "S-S5phr" indicates "in the raw material reaction product". parts by mass of the polysulfide-containing compound per 100 parts by mass of mesogen diol A".

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 (4)

containing a diene rubber and a liquid crystal elastomer,
The liquid crystal elastomer is a particulate liquid crystal polyurethane elastomer having a transition temperature (Ti) from a liquid crystal phase to an isotropic phase of 20° C. or less and having a functional group that reacts with the diene rubber,
A rubber composition, wherein the liquid crystal polyurethane elastomer is a reaction product of a mesogenic group-containing compound having at least an active hydrogen group, an isocyanate compound, a polysulfide-containing compound, and a photopolymerizable group-containing compound. containing a diene rubber and a liquid crystal elastomer,
The liquid crystal elastomer is a particulate liquid crystal polyurethane elastomer having a transition temperature (Ti) from a liquid crystal phase to an isotropic phase of 20° C. or less and having a functional group that reacts with the diene rubber;
A rubber composition, wherein the liquid crystal polyurethane elastomer is a reaction product of a mesogenic group-containing compound having at least an active hydrogen group, an isocyanate compound, a polysulfide-containing compound, and a polyfunctional compound. 3. The rubber composition according to claim 1 , wherein the liquid crystalline elastomer is compounded in an amount of 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 3 .