Patent Application
20130217802
The present invention relates to a method for producing a rubber composition containing an inorganic filler and having an improved low-heat-generation property.
Recently, in association with the movement of global regulation of carbon dioxide emission associated with the increase in attraction to environmental concerns, the demand for low fuel consumption by automobiles is increasing. To satisfy the requirement, it is desired to reduce rolling resistance relating to tire performance. Heretofore, as a means for reducing the rolling resistance of tires, a method of optimizing tire structures has been investigated; however, at present, a technique of using a low-heat-generating rubber composition for tires has become employed as the most common method.
For obtaining such a low-heat-generating rubber composition, there is known a method of using an inorganic filler such as silica or the like.
However, in incorporating an inorganic filler such as silica or the like in a rubber composition to prepare an inorganic filler-containing rubber composition, the inorganic filler, especially silica aggregates in the rubber composition (owing to the hydroxyl group in the surface of silica), and therefore, for preventing the aggregation, a silane coupling agent is used.
Accordingly, for successfully solving the above-mentioned problem by incorporation of a silane coupling agent, various trials have been made for increasing the activity of the coupling function of the silane coupling agent.
For example, Patent Reference 1 proposes a vulcanizable rubber composition containing a rubber polymer, a vulcanizing agent, a filler containing silica, and silane coupling agent, wherein the coupling agent is at least bifunctional and is capable of reacting with silica and the rubber polymer.
Patent Reference 2 proposes a rubber composition that comprises, in 100 parts by weight of a natural rubber and/or a dienic rubber, from 15 to 85 parts by weight of silica, a dispersion improver in an amount of from 1 to 15% by weight of the silica, and a specific silane coupling agent in an amount of from 1 to 15% by weight of the silica.
Patent Reference 3 proposes a rubber composition comprising, in 100 parts by weight of a dienic rubber component (A), from 5 to 150 parts by weight of silica (B) having a nitrogen adsorption specific surface area of from to 300 m2/g, a silane coupling agent (C) having a specific structure and having a mercapto group content of from 1 to 15%, in an amount of from 3 to 15 parts by weight relative to 100 parts by weight of the silica, and from 5 to 20 parts by weight of zinc oxide (D).
Further, Patent Reference 4 proposes a silica-incorporated rubber composition that contains an organic silicon compound having, in the molecule thereof, at least one silicon-oxygen bond and from 1 to 10 sulfur atoms containing at least one linear alkoxy group, and having at least one nitrogen atom in the position spaced from the silicon atom by from 3 to 8 atoms, especially an organic silicon compound having a cyclic structure that contains a nitrogen atom and a silicon atom.
However, in these inventions, nothing is taken into consideration relating to kneading conditions.
As a case of increasing the activity of the coupling function of a silane coupling agent in consideration of kneading conditions, there is mentioned Patent Reference 5; however, it is desired to further improve the effect of enhancing the activity of the coupling function of a silane coupling agent.
Patent Reference 1: JP-A 7-165991
Patent Reference 2: W01997/35918
Patent Reference 3: JP-A 2009-126907
Patent Reference 4: WO2009/104766
Patent Reference 5: WO2008/123306
Given the situation as above, an object of the present invention is to provide a method for producing a rubber composition capable of further increasing the activity of the coupling function of a silane coupling agent to thereby successfully produce a low-heat-generating rubber composition, without lowering the workability of the unvulcanized rubber composition.
For solving the above-mentioned problems, the present inventors have made various investigations of a method of kneading a rubber component, all or a part of an inorganic filler, all or a part of a silane coupling agent, and an acidic and/or basic compound in the first stage of a kneading step therein, and, as a result, have experimentally found that, in order to enhance the activity of the coupling function, it is good to optimize the time at which the acidic and/or basic compound is added, and have completed the present invention.
Specifically, the present invention provides the following:
[1] A method for producing a rubber composition containing a rubber component (A) of at least one selected from natural rubbers and synthetic dienic rubbers, a filler containing an inorganic filler (B), and a silane coupling agent (C) of a compound having a mercapto group, wherein the rubber composition is kneaded in multiple stages, in the first stage of kneading, the rubber component (A), all or a part of the inorganic filler (B), and all or a part of the silane coupling agent (C) are kneaded, then in the first stage or in the subsequent kneading stage, at least one compound selected from an acidic compound (D) and a basic compound (E) is added, and the highest temperature of the rubber composition in the final stage of kneading is from 60 to 120° C.; and
[2] The method for producing a rubber composition according to [1], wherein the mercapto group-having compound is at least one compound selected from a group consisting of compounds represented by the following general formulae (I) and (II):
[In the formula, R1, R2 and R3 each independently represents a group selected from —O—CjH2j+1, —(O—CkH2k—)a—O—CmH2m+1 and —CnH2n+1; j, m and n each independently indicates from 0 to 12; k and a each independently indicates from 1 to 12; R4 represents a group selected from linear, branched or cyclic, saturated or unsaturated alkylene group, cycloalkenylene group, cycloalkylalkylene group, cycloalkenylalkylene group, alkenylene group, cycloalkenylene group, cycloalkylalkenylene group, cycloalkenylalkenylene group, arylene group and aralkylene group, having from 1 to 12 carbon atoms.]
[In the formula, W represents a group selected from —NR6—, —O— and —CR9R10— (where R8 and R9 each represent —CpH2p+1, R10 represents —CqH2q+1, p and q each independently indicates from 0 to 20); R5 and R6 each independently represents -M-CrH2r— (where M represents —O— or —CH2—, and r indicates from 1 to 20); R7 represents a group selected from —O—CjH2j+1, —(O—CkH2k—)a—O—CmH2m+1 and —CnH2n+1; j, m and n each independently indicates from 0 to 12; k and a each independently indicates from 1 to 12; R4 represents a group selected from linear, branched or cyclic, saturated or unsaturated alkylene group, cycloalkylene group, cycloalkylalkylene group, cycloalkenylalkylene group, alkenylene group, cycloalkenylene group, cycloalkylalkenylene group, cycloalkenylalkenylene group, arylene group and aralkylene group, having from 1 to 12 carbon atoms.]
[3] A rubber composition produced according to the rubber composition production method of the above [1]; and
[4] A tire using the rubber composition of the above [3].
According to the present invention, there is provided a method for producing a rubber composition capable of further increasing the activity of the coupling function of a silane coupling agent to produce a rubber composition excellent in low-heat-generation property, without lowering the workability of the unvulcanized rubber composition.
The present invention is described in detail hereinunder.
The method for producing a rubber composition of the present invention is a method for producing a rubber composition containing a rubber component (A) of at least one selected from natural rubbers and synthetic dienic rubbers, a filler containing an inorganic filler (B), and a silane coupling agent (C) of a compound having a mercapto group, wherein the rubber composition is kneaded in multiple stages, in the first stage of kneading, the rubber component (A), all or a part of the inorganic filler (B), and all or a part of the silane coupling agent (C) are kneaded, then in the first stage or in the subsequent kneading stage, at least one compound selected from an acidic compound (D) and a basic compound (E) is added, and the highest temperature of the rubber composition in the final stage of kneading is from 60 to 120° C.
Here, the mercapto group-having compound is preferably at least one compound selected from a group consisting of compounds represented by the following general formulae (I) and (II):
In the formula, R1, R2 and R3 each independently represents a group selected from —O—CjH2j+1, —(O—CkH2k—)a—O—CmH2m+1 and —CnH2n+1; j, m and n each independently indicates from 0 to 12; k and a each independently indicates from 1 to 12; R4 represents a group selected from linear, branched or cyclic, saturated or unsaturated alkylene group, cycloalkylene group, cycloalkylalkylene group, cycloalkenylalkylene group, alkenylene group, cycloalkenylene group, cycloalkylalkenylene group, cycloalkenylalkenylene group, arylene group and aralkylene group, having from 1 to 12 carbon atoms.
Preferably, at least one of R1, R2 and R3 is —(O—CkH2k—)a—O—CmH2m+1.
In the formula, W represents a group selected from —NR8—, —O— and —CR9R10— (where R8 and R9 each represent —CpH2p+1, R10 represents —CqH2q+1, p and q each independently indicates from 0 to 20); R5 and R6 each independently represents -M-CrH2r— (where M represents —O— or —CH2—, and r indicates from 1 to 20); R7 represents a group selected from —O—CjH2j+1, —(O—CkH2k—)a—O—CmH2m+1 and —CnH2n+1; j, m and n each independently indicates from 0 to 12; k and a each independently indicates from 1 to 12; R4 represents a group selected from linear, branched or cyclic, saturated or unsaturated alkylene group, cycloalkylene group, cycloalkylalkylene group, cycloalkenylalkylene group, alkenylene group, cycloalkenylene group, cycloalkylalkenylene group, cycloalkenylalkenylene group, arylene group and aralkylene group, having from 1 to 12 carbon atoms.
In the present invention, after the rubber component (A), all or a part of the inorganic filler (B), and all or a part of the silane coupling agent (C) are kneaded in the first stage of kneading, and then in the first stage or in the subsequent kneading stage, at least one compound selected from an acidic compound (D) and a basic compound (E) is added; and this is in order to enhance the activity of the coupling function of the silane coupling agent (C). Specifically, after the reaction of the inorganic filler (B) and the silane coupling agent (C) has fully gone on, the reaction of the silane coupling agent (C) and the rubber component (A) can be go on.
The highest temperature of the rubber composition in the final stage of kneading is preferably from 80 to 120° C., and this is for securing good dispersion of the chemicals to be added in the final stage. From this viewpoint, the temperature is more preferably from 100 to 120° C.
In the present invention, the first stage of kneading is the initial stage of kneading the rubber component (A), all or a part of the inorganic filler (B), and all or a part of the silane coupling agent (C), but does not include a case of kneading the rubber component (A) and the other filler than the inorganic filler (B) in the initial stage and a case of pre-kneading the rubber component (A) alone.
It is desirable that the highest temperature of the rubber composition in the first stage of kneading is from 120 to 190° C. for more successfully enhancing the activity of the coupling function of the silane coupling agent (C).
In the present invention, it is desirable that the acidic compound (D) is added in the kneading stage after the first stage of kneading for more successfully enhancing the activity of the coupling function of the silane coupling agent (C). For the same reason, it is desirable that the basic compound (E) is added in the kneading stage after the first stage of kneading, and more preferably, the acidic compound (D) and the basic compound (E) are added in the final stage of kneading.
For more successfully enhancing the activity of the coupling function of the silane coupling agent (C), it is also desirable to add the acidic compound (D) in the kneading stage after the kneading stage where the basic compound (E) is added.
In the present invention, the acidic compound (D) is used as a sulfur vulcanization activator, and for example, in the final stage of kneading, if desired, a suitable amount of the compound may be incorporated.
The silane coupling agent (C) for use in the rubber composition production method of the present invention is a compound having a mercapto group. The mercapto group-having compound is preferably at least one compound selected from a group consisting of compounds represented by the above-mentioned general formulae (I) and (II).
In the general formulae (I) and (II), specific examples of R1, R2, R3 and R7 include, for example, a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a hydroxy group, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a hydrogen atom, etc. Above all, preferred are a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a methyl group, an ethyl group, a propyl group, an isopropyl group, etc.
Specific examples of R4 include, for example, a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a nonylene group, a decylene group, an undecylene group, a dodecylene group, etc.
Specific examples of R5 and R6 include, for example, a propylene group, an ethylene group, a hexylene group, a butylene group, a methylene group, etc.
Compounds represented by the general formula (I) include, for example, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, (mercaptomethyl)dimethylethoxysilane, mercaptomethyltrimethoxysilane, etc.
Compounds represented by the general formula (II) include, for example, 3-mercaptopropyl(ethoxy)-1,3-dioxa-6-methylaza-2-silacyclooctane, 3-mercaptopropyl(ethoxy)-1,3-dioxa-6-butylaza-2-silacyclooctane, 3-mercaptopropyl(ethoxy)-1,3-dioxa-6-dodecylaza-2-silacyclooctane, etc.
Using the silane coupling agent (C) of the type, the rubber composition in the present invention can give pneumatic tires more excellent in low-heat-generation property having better abrasion resistance.
In the present invention, one alone or two or more different types of the silane coupling agents (C) can be used either singly or as combined.
Regarding the amount of the silane coupling agent (C) to be in the rubber composition in the present invention, preferably, the ratio by mass of {silane coupling agent (C)/inorganic filler (B)} is from (1/100) to (20/100). When the ratio is at least (1/100), then the effect of enhancing the low-heat-generation property of the rubber composition can be more successfully exhibited; and when at most (20/100), the cost of the rubber composition is low and the economic potential thereof increases. Further, the ratio by mass is more preferably from (3/100) to (20/100), even more preferably from (4/100) to (15/100).
Not specifically defined, the acidic compound (D) for use in the present invention may be any acidic compound, but is preferably a mono- or poly-organic acid, or a partial ester of a poly-organic acid, or a metal salt of a mono- or poly-organic acid.
The mono-organic acid includes saturated fatty acids and unsaturated fatty acids such as stearic acid, palmitic acid, myristic acid, lauric acid, arachidic acid, behenic acid, lignoceric acid, capric acid, pelargonic acid, caprylic acid, enanthic acid, caproic acid, oleic acid, vaccenic acid, linolic acid, linolenic acid, nervonic acid, etc.; as well as resin acids such as rosin acids (abietic acid, neoabietic acid, dehydroabietic acid, paralustrinic acid, pimaric acid, isopimaric acid, etc.), modified rosin acids, etc.
The poly-organic acid includes unsaturated dicarboxylic acids or saturated dicarboxylic acids, as well as their partial esters (for example, monoesters) or acid anhydrides, etc.
The unsaturated dicarboxylic acid includes maleic acid, fumaric acid, citraconic acid, mesaconic acid, 2-pentene diacid, methylenesuccinic acid (itaconic acid), allylmalonic acid, isopropylidenesuccinic acid, 2,4-hexadiene diacid, acetylene-dicarboxylic acid, etc.; and the saturated dicarboxylic acid includes oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, tridecene diacid, methylsuccinic acid, 2,2-dimethylsuccinic acid, 2,3-dimethylsuccinic acid, tetramethylsuccinic acid, etc.
As the partial ester, preferably mentioned are (poly)esters of an unsaturated carboxylic acid and an oxycarboxylic acid; esters having a carboxyl group at both ends thereof, of a diol such as ethylene glycol, hexanediol, cyclohexanedimethanol or the like and an unsaturated dicarboxylic acid such as maleic acid, fumaric acid, itaconic acid or the like; etc.
The oxycarboxylic acid includes malic acid, tartaric acid, citric acid, etc.
The (poly)ester of an unsaturated carboxylic acid and an oxycarboxylic acid is preferably maleic acid monoesters, and more preferably monomalate of maleic acid.
The ester having a carboxyl group at both ends thereof, of a diol and an unsaturated dicarboxylic acid includes polyalkylene glycol/maleic acid polyester terminated with a carboxylic acid at both ends, such as polybutylene maleate having a carboxyl group at both ends thereof, poly(PEG200) maleate having a carboxyl group at both ends thereof, etc.; polybutylene adipate maleate having a carboxyl group at both ends thereof, etc.
In the present invention, the acidic compound (D) must fully exhibit the function thereof as a vulcanization activator, and therefore the acidic compound (D) is preferably stearic acid.
Not specifically defined, the basic compound (E) for use in the present invention may be any basic compound, but is preferably various amine-type antiaging agents. Concretely, mentioned are p-phenylenediamine-type antiaging agents such as N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine, N-phenyl-N′-(1-methylheptyl)-p-phenylenediamine, N-phenyl-N′-isopropyl-p-phenylenediamine, N,N′-diphenyl-p-phenylenediamine, N,N′-di-2-naphthyl-p-phenylenediamine, N-phenyl-N′-(3-metharcyloyloxy-2-hydroxypropyl)-p-phenylenedimaine, etc.; diphenylamine-type antiaging agents such as di-tert-butyl-diphenylamine, 4,4′-dicumyl-diphenylamine, alkylated diphenylamines (octylated diphenylamine, etc.), N-phenyl-1-naphthylamine, 4,4′-(α,-α-dimethylbenzyl)-diphenylamine, etc. Above all, preferred is at least one compound selected from a group consisting of N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine, N-phenyl-N′-(1-methylheptyl)-p-phenylenediamine, N-phenyl-N′-isopropyl-p-phenylenediamine, N,N′-diphenyl-p-phenylenediamine, N,N′-di-2-naphthyl-p-phenylenediamine and N-phenyl-N′-(3-methacryloyloxy-2-hydroxypropyl)-p-phenylenediamine; or that is, preferred is such a p-phenylenediamine-type antiaging agent.
In case where the basic compound (E) is added in the first stage of kneading in the present invention, it is desirable that the number of molecules (molar number) of the basic compound (E) in the rubber composition is from 0 to 0.6 times the number of molecules (molar number) of the silane coupling agent (C). When the molar number is at most 0.6 times, the reaction between the silane coupling agent (C) and silica can be successfully prevented from being retarded. More preferably, the number of molecules (molar number) of the basic compound (E) is from 0 to 0.4 times the number of molecules (molar number) of the silane coupling agent (C).
In the present invention, the basic compound (E) serves as an antiaging agent, and therefore, if desired, a suitable amount of the compound may be incorporated in the kneading stage after the first stage of kneading, for example, in the final stage of kneading.
As the synthetic dienic rubber of the rubber component (A) for use in the rubber composition production method of the present invention, usable here are styrene-butadiene copolymer rubber (SBR), polybutadiene rubber (BR), polyisoprene rubber (IR), butyl rubber (IIR), ethylene-propylene-diene tercopolymer rubber (EPDM), etc. One or more different types of natural rubbers and synthetic dienic rubbers may be used here either singly or as combined.
In the rubber composition production method of the present invention, it is desirable that a synthetic rubber produced according to a solution polymerization method (for example, solution-polymerized SBR, solution-polymerized BR, etc.) accounts for at least 70% by mass of the rubber component (A), more preferably at least 80% by mass, even more preferably at least 90% by mass. Especially preferably, the rubber component (A) is entirely a synthetic rubber produced according to a solution polymerization method. This is in order to reduce the influence of at least one compound selected from the acidic compound (D) and the basic compound (E) derived from the emulsifier contained in the synthetic rubber produced according to an emulsion polymerization method.
As the inorganic filler (B) for use in the rubber composition production method of the present invention, usable are silica and an inorganic compound represented by the following general formula (III):
dM1.xSiOy.zH2O (III)
In the general formula (III), M1 represents at least one selected from a metal selected from aluminium, magnesium, titanium, calcium and zirconium, and oxides or hydroxides of those metals, their hydrates, or carbonates of the metals; d, x, y and z each indicates an integer of from 1 to 5, an integer of from 0 to 10, an integer of from 2 to 5, and an integer of from 0 to 10, respectively.
In the general formula (III), when x and z are both 0, then the inorganic compound is at least one metal selected from aluminium, magnesium, titanium, calcium and zirconium, or a metal oxide or metal hydroxide thereof.
In the present invention, silica is preferred as the inorganic filler (B) from the viewpoint of satisfying both low rolling property and abrasion resistance. As silica, any commercially-available one is usable here; and above all, preferred is wet silica, dry silica or colloidal silica, and more preferred is wet silica. Preferably, the BET specific surface area (as measured according to ISO 5794/1) of silica for use herein is from 40 to 350 m2/g. Silica of which the BET specific surface area falls within the range is advantageous in that it satisfies both rubber-reinforcing capability and dispersibility in rubber component. From this viewpoint, silica of which the BET specific surface area falls within a range of from 80 to 350 m2/g is more preferred; silica of which the BET specific surface area falls within a range of more than 130 m2/g to 350 m2/g is even more preferred; and silica of which the BET specific surface area falls within a range of from 135 to 350 m2/g is even more preferred. As silicas of those types, usable here are commercial products of Tosoh Silica's trade names “Nipseal AQ” (BET specific surface area=205 m2/g) and “Nipseal KQ” (BET specific surface area=240 m2/g); Degussa's trade name “Ultrasil VN3” (BET specific surface area=175 m2/g), etc.
As the inorganic compound represented by the general formula (III), usable here are alumina (Al2O3) such as γ-alumina, α-alumina, etc.; alumina monohydrate (Al2O3.H2O) such as boehmite, diaspore, etc.; aluminium hydroxide [Al(OH)3] such as gypsite, bayerite, etc.; aluminium carbonate [Al2(CO3)2], magnesium hydroxide [Mg(OH)2], magnesium oxide (MgO), magnesium carbonate (MgCO3), talc (3MgO.4SiO2.H2O), attapulgite (5MgO.8SiO2.9H2O), titanium white (TiO2), titanium black (TiO2n-1), calcium oxide (CaO), calcium hydroxide [Ca(OH)2], aluminium magnesium oxide (MgO.Al2O3), clay (Al2O3.2SiO2), kaolin (Al2O3.2SiO2.2H2O), pyrophyllite (Al2O3.4SiO2.H2O), bentonite (Al2O3.4SiO2.2H2O), aluminium silicate (Al2SiO5, Al4.3SiO4.5H2O, etc.), magnesium silicate (Mg2SiO4, MgSiO3, etc.), calcium silicate (Ca2.SiO4, etc.), aluminium calcium silicate (Al2O3.CaO.2SiO2, etc.), magnesium calcium silicate (CaMgSiO4), calcium carbonate (CaCO3), zirconium oxide (ZrO2), zirconium hydroxide [ZrO(OH)2.nH2O], zirconium carbonate [Zr(CO3)2]; as well as crystalline aluminosilicate salts containing a charge-correcting hydrogen, alkali metal or alkaline earth metal such as various types of zeolite. Preferably, M3 in the general formula (5) is at least one selected from aluminium metal, aluminium oxide or hydroxide, and their hydrates, or aluminium carbonate.
One or more different types of the inorganic compounds of the general formula (III) may be used here either singly or as combined. The mean particle size of the inorganic compound is preferably within a range of from 0.01 to 10 μm from the viewpoint of the balance of kneading workability, abrasion resistance and wet grip performance, and more preferably within a range of from 0.05 to 5 μm.
As the inorganic filler (B) in the present invention, silica alone may be used, or silica as combined with at least one inorganic compound of the general formula (III) may be used.
If desired, the filler in the rubber composition in the present invention may contain carbon black in addition to the above-mentioned inorganic filler (B). Containing carbon black, the filler enjoys the effect of lowering the electric resistance of the rubber composition to thereby prevent static electrification thereof. Carbon black for use herein is not specifically defined. For example, preferred is use of high, middle or low-structure SAF, ISAF, IISAF, N339, HAF, FEF, GPF, SRF-grade carbon black; and more preferred is use of SAF, ISAF, IISAF, N339, HAF, FEF-grade carbon black. Preferably, the nitrogen adsorption specific surface area (N2SA, as measured according to JIS K 6217-2:2001) of such carbon black is from 30 to 250 m2/g. One alone or two or more different types of such carbon black may be used here either singly or as combined. In the present invention, the inorganic filler (B) does not contain carbon black.
The inorganic filler (B) in the rubber composition in the present invention is preferably in an amount of from 20 to 120 parts by mass relative to 100 parts by mass of the rubber component (A). When the amount is at least 20 parts by mass, then it is favorable from the viewpoint of securing wet performance; and when at most 120 parts by mass, then it is favorable from the viewpoint of reducing rolling resistance. Further, the amount is more preferably from 30 to 100 parts by mass.
Also preferably, the filler in the rubber composition in the present invention is in an amount of from 20 to 150 parts by mass relative to 100 parts by mass of the rubber component (A). When the amount is at least 20 parts by mass, then it is favorable from the viewpoint of enhancing rubber composition reinforcing capability; and when at most 150 parts by mass, then it is favorable from the viewpoint of reducing rolling resistance.
In the filler, preferably, the amount of the inorganic filler (B) is at least 30% by mass from the viewpoint of satisfying both wet performance and reduced rolling resistance, more preferably at least 40% by mass, and even more preferably at least 70% by mass.
In case where silica is used as the inorganic filler (B), it is desirable that silica accounts for at least 30% by mass of the filler, more preferably at least 35% by mass.
In the rubber composition production method of the present invention, various additives that are generally incorporated in a rubber composition, for example, a vulcanization activator such as zinc flower or the like, an antiaging agent and others may be optionally added and kneaded in the first stage or the final stage of kneading, or in the intermediate stage between the first stage and the final stage.
As the kneading apparatus for the production method of the present invention, usable is any of a Banbury mixer, a roll, an intensive mixer, a kneader, a double-screw extruder, etc.
The present invention is described in more detail with reference to the following Examples; however, the present invention is not limited at all by the following Examples.
The highest temperature of the rubber composition in kneading stage, the Mooney viscosity (ML1+4) index and the low-heat-generation property (tanδ index) were evaluated according to the following methods.
Measurement Method for Highest Temperature of Rubber Composition in First Stage and Final Stage of Kneading
A thermometer was inserted into the center part of the rubber composition immediately after taken out of a Banbury mixer, and the temperature of the composition was measured. One sample was measured three times, and the arithmetic average thereof was referred to as the highest temperature.
The Mooney viscosity (ML1+4/130° C.) was measured at 130° C. according to JIS K 6300-1:2001, and shown as index indication according to the following formula. The samples having a smaller index have a lower viscosity and therefore have better workability.
Mooney Viscosity (ML1+4) Index=(Mooney viscosity of unvulcanized rubber composition tested)/(Mooney viscosity of unvulcanized rubber composition of Comparative Example 1, 19, 27, 35 or 43)
Low-Heat-Generation Property (tanδ index)
Using a viscoelasticity measuring device (by Rheometric), tanδ of the rubber composition sample was measured at a temperature of 60° C., at a dynamic strain of 5% and at a frequency of 15 Hz. Based on the reciprocal of tanδ in Comparative Example 1, 19, 27, 35 or 43, as referred to 100, the data were expressed as index indication according to the following formula. The samples having a larger index value have a better low-heat-generation property and have a smaller hysteresis loss.
Low-Heat-Generation Index={(tanδ of vulcanized rubber composition of Comparative Example 1)/(tanδ of vulcanized rubber composition tested)}×100
In a nitrogen atmosphere in a 500-mL four-neck eggplant flask, 23.8 g of 3-mercaptopropyltriethoxysilane, 11.9 g of N-methyldiethanolamine and 0.05 g of titanium tetra-n-butoxide were dissolved in 200 mL of xylene. This was heated up to 150° C. and stirred for 6 hours. Subsequently, using a rotary evaporator, the solvent was evaporated away at 20 hPa/40° C., and then via a rotary pump (10 Pa) and a cold trap (dry ice+ethanol), the remaining volatiles were removed to give 24.0 g of 3-mercaptopropyl(ethoxy)-1,3-dioxa-6-methylaza-2-silacyclooctane.
1H-NMR (CDCl3, 700 MHz, δ; ppm)=3.7(m;6H), 2.6(t;4H), 2.5(m;2H), 2.4(s;3H), 1.6(m;2H), 0.8(t;3H), 0.6(t;2H)
In a nitrogen atmosphere in a 500-mL four-neck eggplant flask, 23.8 g of 3-mercaptopropyltriethoxysilane, 16.1 g of N-butyldiethanolamine and 0.05 g of titanium tetra-n-butoxide were dissolved in 200 mL of xylene. This was heated up to 150° C. and stirred for 6 hours. Subsequently, using a rotary evaporator, the solvent was evaporated away at 20 hPa/40° C., and then via a rotary pump (10 Pa) and a cold trap (dry ice+ethanol), the remaining volatiles were removed to give 28.7 g of 3-mercaptopropyl(ethoxy)-1,3-dioxa-6-butylaza-2-silacyclooctane.
1H-NMR (CDCl3, 700 MHz, δ; ppm)=3.7(m;6H), 2.6(t;4H), 2.5(m;2H), 2.4(m;2H), 1.6(m;2H), 1.4(m;2H), 1.3(m;2H), 0.9(t;3H), 0.8(t;3H), 0.6(t;2H)
In a nitrogen atmosphere in a 500-mL four-neck eggplant flask, 23.8 g of 3-mercaptopropyltriethoxysilane, 27.3 g of N-lauryldiethanolamine and 0.05 g of titanium tetra-n-butoxide were dissolved in 200 mL of xylene. This was heated up to 150° C. and stirred for 6 hours. Subsequently, using a rotary evaporator, the solvent was evaporated away at 20 hPa/40° C., and then via a rotary pump (10 Pa) and a cold trap (dry ice+ethanol), the remaining volatiles were removed to give 40.0 g of 3-mercaptopropyl(ethoxy)-1,3-dioxa-6-dodecylaza-2-silacyclooctane.
1H-NMR (CDCl3, 700 MHz, δ; ppm)=3.7(m;6H), 2.6(t;4H), 2.5(m;2H), 2.4(m;2H), 1.6(m;2H), 1.4(m;2H), 1.3(m;18H), 0.9(t;3H), 0.8(t;3H), 0.6(t;2H)
According to the compositional formulation and the kneading method shown in Tables 1 to 4, the rubber component, silica, the silane coupling agent and others were added and kneaded in the first stage of kneading. In Examples 1 to 18 and 29 to 36 and Comparative Examples 1 to 12 and 15 to 18 shown in Tables 1, 2 and 4, the highest temperature of the rubber composition in the first stage of kneading was controlled at 150° C. In Examples 19 to 28 and Comparative Example 13 and 14 shown in Table 3, the highest temperature of the rubber composition in the first stage of kneading was controlled as in Table 3. In Comparative Examples 1 to 18, at least one compound selected from the acidic compound (D) and the basic compound (E) was added along simultaneously with the silane coupling agent in the first stage of kneading.
Next, the highest temperature of the rubber composition in the final stage of kneading was controlled as in Tables 1 to 4. In each stage of kneading, a Banbury mixer was used for the kneading. The obtained 54 rubber compositions were evaluated in point of the Mooney viscosity (ML1+4) index and the low-heat-generation property (tanδ index) thereof according to the above-mentioned methods. The results are shown in Tables 1 to 4.
In Tables 1 to 4, the acidic compound (D) is abbreviated as “organic acid” and the basic compound (E) is as “base”.
According to the compositional formulation and the kneading method shown in Table 5, the rubber component, silica, the silane coupling agent and others were added and kneaded in the first stage of kneading. The highest temperature of the rubber composition in the first stage of kneading was controlled at 150° C. Next, in the second stage of kneading, at least one compound selected from the acidic compound (D) and the basic compound (E) shown in Table 5 was added. Next, the highest temperature of the rubber composition in the final stage of kneading was controlled as in Table 5. In each stage of kneading, a Banbury mixer was used for the kneading. The obtained 3 rubber compositions were evaluated in point of the Mooney viscosity (M1+4) index and the low-heat-generation property (tanδ index) thereof according to the above-mentioned methods. The results are shown in Table 5. For comparison, the data of Examples 1 and 9 and Comparative Example 1 were again shown therein.
In Table 5, the acidic compound (D) is abbreviated as “organic acid” and the basic compound (E) is as “base”. *1 to *11 are the same as in [Notes] for Tables 1 to 4.
According to the compositional formulation and the kneading method shown in Tables 6 to 9, the rubber component, silica, the silane coupling agent and others were added and kneaded in the first stage of kneading. In Examples 40 to 79 and Comparative Examples 19 to 50 shown in Tables 6 to 9, the highest temperature of the rubber composition in the first stage of kneading was controlled at 150° C. In Comparative Examples 19 to 50, at least one compound selected from the acidic compound (D) and the basic compound (E) was added simultaneously with the silane coupling agent in the first stage of kneading.
Next, the highest temperature of the rubber composition in the final stage of kneading was controlled as in Tables 6 to 9. In each stage of kneading, a Banbury mixer was used for the kneading. The obtained 72 rubber compositions were evaluated in point of the Mooney viscosity (ML1+4) index and the low-heat-generation property (tanδ index) thereof according to the above-mentioned methods. The results are shown in Tabled 6 to 9.
In Tables 6 to 9, the acidic compound (D) is abbreviated as “organic acid” and the basic compound (E) is as “base”.
As obvious from Tables 1 to 9, the rubber compositions of Examples 1 to 79 are all better than the comparative rubber compositions of Comparative Examples 1 to 50 in point of the workability of the unvulcanized rubber composition and the low-heat-generation property (tanδ index).
According to the production method for a rubber composition of the present invention, it is possible to obtain a rubber composition excellent in low-heat-generation property with further enhancing the coupling function activity thereof without lowering the workability of the unvulcanized rubber composition, and is therefore favorably used as a production method for constitutive members of various types of pneumatic tires for passenger cars, small-size trucks, minivans, pickup trucks and big-size vehicles (trucks, buses, construction vehicles, etc.) and others, especially for tread members of pneumatic radial tires.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-224364 | Oct 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/072793 | 10/3/2011 | WO | 00 | 5/2/2013 |
