JP6219205B2 - Method for producing rubber composition - Google Patents

Description

  The present invention relates to a method for producing a rubber composition.

  Conventionally, for example, in rubber compositions used for pneumatic tires, it has been required to reduce rolling resistance by making it difficult to generate heat, that is, to improve rolling resistance performance. Further, there are cases where it is required to improve the grip performance (that is, wet grip performance) on a wet road surface while improving the rolling resistance performance, or to increase the hardness to improve steering stability. Since these performances are in contradiction, it is difficult to satisfy them at the same time.

  In order to improve rolling resistance performance, a technique has been developed in which silica is used as a filler and a silane coupling agent is added to improve the dispersibility. In order to improve the properties of such a silica-blended rubber composition, it is known to blend a substance that improves the reactivity between silica and a silane coupling agent. For example, Patent Document 1 discloses using an imidazole compound as a reaction promoting compound between silica and a silane coupling agent. Patent Document 2 discloses using an imidazole compound as a catalyst for the alkoxysilane-silica reaction. In these documents, substituted imidazoles such as 2-heptadecylimidazole are listed together with unsubstituted imidazole as imidazole compounds.

  The imidazole compound is added to and mixed with the diene rubber together with silica and a silane coupling agent in a first mixing step called non-pro kneading. At that time, when zinc white is added together, the effect of the imidazole compound is impaired. Therefore, in the examples described in Patent Documents 1 and 2, zinc white is sulfur in the final mixing step called pro-kneading. And added together with a vulcanization accelerator.

International Publication No. 2008/123306 Special table 2008-537740 gazette

  However, since zinc white is generally difficult to disperse, when added in the final mixing step, general physical properties such as breaking strength may be impaired due to poor dispersion of zinc white itself. Therefore, when blending an imidazole compound, it is desired to increase the dispersibility improvement effect of silica by the imidazole compound while suppressing a decrease in dispersibility of zinc white.

  The present invention has been made in view of the above points, and provides a method for producing a rubber composition capable of enhancing the effect of improving the dispersibility of silica by an imidazole compound while suppressing a decrease in dispersibility of zinc white. With the goal.

  The method for producing a rubber composition according to the present invention is based on 100 parts by mass of diene rubber, 20 to 120 parts by mass of silica, 2 to 20% by mass of a silane coupling agent based on the amount of silica, and 12 or more carbon atoms. Obtained by the first mixing step and the first mixing step, in which 0.2 to 3 parts by mass of a hydrophobic imidazole having a saturated or unsaturated hydrocarbon group bonded to the 2-position of the imidazole ring and zinc white are mixed. And a second mixing step of adding and mixing sulfur and a vulcanization accelerator to the mixture.

  ADVANTAGE OF THE INVENTION According to this invention, the dispersibility improvement effect of the silica by an imidazole compound can be heightened, suppressing the dispersibility fall of zinc white.

  Hereinafter, matters related to the implementation of the present invention will be described in detail.

  In the method for producing a rubber composition according to the present embodiment, silica, a silane coupling agent, and a saturated or unsaturated hydrocarbon group having 12 or more carbon atoms are bonded to the 2-position of the imidazole ring with respect to the diene rubber. A first mixing step of mixing the hydrophobic imidazole and zinc white, and a second mixing step of adding and mixing sulfur and a vulcanization accelerator to the mixture obtained in the first mixing step. .

  The reaction between silica and the silane coupling agent proceeds by a bimolecular nucleophilic substitution reaction (SN2). At this time, if an imidazole compound which is a weak base excellent in nucleophilicity / elimination is present, the progress of the reaction can be facilitated, and a rubber composition having reduced rolling resistance can be obtained. Such an effect can be obtained with other nitrogen-containing compounds, but many of them have strong basicity, so that the scorch time tends to be too short. If it is an imidazole compound, rolling resistance performance can be improved, suppressing the fall of scorch property.

  In this embodiment, a hydrophobic imidazole substituted with a hydrocarbon group having 12 or more carbon atoms is used as the imidazole compound. Hydrophobic imidazole is considered to promote the dispersion of silica by exerting the same effect as a surfactant in rubber by arranging a hydrophilic imidazole group and a hydrophobic group at both ends. Will improve the balance of rolling resistance performance, wet grip performance and hardness. Such an effect has not been known so far and has been found for the first time by the present inventors.

  Moreover, in the case of an unsubstituted imidazole or an imidazole compound substituted with a hydrocarbon group having a small number of carbon atoms, there is a problem that the effect is reduced when zinc white is added together as described above. New knowledge that such a problem does not occur was obtained. That is, when it is a hydrophobic imidazole, it is presumed that the binding between the nitrogen atom of the imidazole ring and zinc white is suppressed by the steric hindrance by the hydrocarbon group which is the 2-position substituent. Even when added in the same mixing step, the effect of the hydrophobic imidazole can be effectively exhibited. Therefore, by adding zinc white in the first mixing step, the dispersibility of zinc white can be improved, and a decrease in general physical properties such as breaking strength can be suppressed.

  In the present embodiment, the diene rubber as the rubber component is not particularly limited. For example, natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), styrene -Isoprene rubber, butadiene-isoprene rubber, styrene-butadiene-isoprene rubber, nitrile rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), etc., and these may be used alone or in combination of two or more. Can be used. More preferably, it is at least one selected from the group consisting of NR, SBR and BR.

In the present embodiment, the silica is not particularly limited, but wet silica such as wet precipitation silica or wet gel silica is preferably used. Colloidal properties of the silica is not particularly limited, for example, (measured according to BET method according to JIS K6430) BET specific surface area may also be used as a 80~300m ² / g, 150~230m ² / You may use what is g. The compounding quantity of a silica is 20-120 mass parts with respect to 100 mass parts of said diene rubbers, and can be suitably set according to a use. More preferably, it is 30-100 mass parts, More preferably, it is 40-90 mass parts.

In the present embodiment, silica may be used alone as the reinforcing filler, or silica and carbon black may be used in combination. The carbon black is not particularly limited, and various known varieties can be used. For example, carbon black having a nitrogen adsorption specific surface area (N ₂ SA) (JIS K6217-2) of 35 to 150 m ² / g is used. Specifically, SAF class (N100 series), ISAF class (N200 series), HAF class (N300 series), and FEF class (N500 series) (both are ASTM grade) are preferably used. The compounding quantity of carbon black is not specifically limited, For example, 50 mass parts or less may be sufficient with respect to 100 mass parts of said diene rubbers, and 5-30 mass parts may be sufficient. In a preferred embodiment, the amount of carbon black is less than the amount of silica.

  In this embodiment, as a silane coupling agent, the various silane coupling agents currently used as a silane coupling agent for rubber | gum can be used, It does not specifically limit. For example, bis (3-triethoxysilylpropyl) tetrasulfide, bis (3-triethoxysilylpropyl) disulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis (4-triethoxysilylbutyl) disulfide, bis ( Sulfide silanes such as 3-trimethoxysilylpropyl) tetrasulfide and bis (2-trimethoxysilylethyl) disulfide; 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3 -Mercaptosilane such as mercaptopropyldimethylmethoxysilane, mercaptoethyltriethoxysilane; 3-octanoylthio-1-propyltriethoxysilane, 3-propionylthiopropylto Examples include various sulfur-containing silane coupling agents such as protected mercaptosilanes such as limethoxysilane (that is, silane compounds having a thiol ester structure in which the mercapto group is protected by an acyl group). , Or a combination of two or more.

  The compounding quantity of a silane coupling agent is 2-20 mass% with respect to the silica compounding quantity. That is, it is preferable that a silane coupling agent is mix | blended in 2-20 mass parts with respect to 100 mass parts of silica. The compounding amount of the silane coupling agent is more preferably 3 to 15% by mass, further preferably 5 to 12% by mass with respect to the silica compounding amount.

  The hydrophobic imidazole used in this embodiment has a saturated or unsaturated hydrocarbon group having 12 or more carbon atoms as a substituent, and the substituent is bonded to the carbon atom at the 2-position of the imidazole ring. By substituting with a hydrocarbon group having 12 or more carbon atoms, it is possible to impart sufficient hydrophobicity to exert a surfactant-like action in the rubber and to react with zinc white due to its steric hindrance. It can be suppressed. It is preferable that carbon number of a substituent is 13-21, More preferably, it is C15-19, More preferably, it is C16-18. The hydrocarbon group is preferably an aliphatic hydrocarbon group such as an alkyl group or an alkenyl group, which may be linear or branched. More preferred is an alkyl group, and even more preferred is an n-alkyl group. A preferable embodiment of the substituent includes an alkyl group having 15 to 19 carbon atoms. Specific examples of the hydrophobic imidazole include, for example, 2-dodecylimidazole, 2-tridecylimidazole, 2-tetradecylimidazole, 2-pentadecylimidazole, 2-hexadecylimidazole, 2-heptadecylimidazole, 2-octadecylimidazole, Examples include 2-nonadecyl imidazole and 2-eicosyl imidazole, and these can be used alone or in combination of two or more. Among these, 2-heptadecylimidazole is particularly preferable.

  The blending amount of the hydrophobic imidazole is preferably 0.2 to 3 parts by mass with respect to 100 parts by mass of the diene rubber, and by setting within such a range, rolling resistance performance and wet grip performance The effect of improving the balance of hardness can be enhanced. The blending amount of the hydrophobic imidazole is more preferably 0.5 to 2.5 parts by mass, still more preferably 0.5 to 2 parts by mass.

  In this embodiment, as zinc white (zinc oxide), various zinc whites generally used as a vulcanization acceleration aid in sulfur vulcanization of diene rubber can be used, and active zinc having a large specific surface area. Hana may be used. Although the compounding quantity of zinc white is not specifically limited, It is preferable that it is 0.5-15 mass parts with respect to 100 mass parts of said diene rubbers, More preferably, it is 1-5 mass parts.

  In this embodiment, stearic acid may be blended. Although the compounding quantity of a stearic acid is not specifically limited, It is preferable that it is 0.5-10 mass parts with respect to 100 mass parts of said diene rubbers, More preferably, it is 1-5 mass parts.

  In the present embodiment, the sulfur as the vulcanizing agent is not particularly limited, and examples thereof include powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur, each of which is independent or Two or more kinds can be mixed and used. It is preferable that the usage-amount of sulfur is 0.1-10 mass parts with respect to 100 mass parts of said diene rubbers, More preferably, it is 0.5-5 mass parts.

  In the present embodiment, the vulcanization accelerator is not particularly limited. For example, N-cyclohexyl-2-benzothiazolylsulfenamide (CBS), N-tert-butyl-2-benzothiazolylsulfenamide ( Sulfenamides such as BBS), N-oxydiethylene-2-benzothiazolylsulfenamide (OBS), N, N-diisopropyl-2-benzothiazolylsulfenamide (DPBS); tetramethylthiuram disulfide (TMTD) ), Thiurams such as tetrabutylthiuram disulfide (TBTD); guanidines such as 1,3-diphenylguanidine (DPG) and 1,3-di-o-tolylguanidine (DOTG); dibenzothiazolyl disulfide (MBTS) , 2-mercaptobenzothiazole (MB ) Thiazole like; N, N'- diphenyl thiourea, trimethylthiourea, N, and the like thiourea such as N'- diethyl thiourea. These can be used alone or in combination of two or more. It is preferable that the compounding quantity of a vulcanization accelerator is 0.1-7 mass parts with respect to 100 mass parts of the said diene rubber, More preferably, it is 0.5-5 mass parts.

  In the present embodiment, in addition to the above components, the rubber composition is blended with various additives usually used in the rubber industry, such as softeners such as process oils, plasticizers, anti-aging agents, waxes and resins. be able to.

  According to the production method of the present embodiment, first, in the first mixing step, silica, a silane coupling agent, a hydrophobic imidazole, and zinc white are added to the diene rubber and mixed (ie, kneaded). To do. The amount of each component is as described above. The first mixing step is an operation generally referred to as non-pro kneading. Therefore, it mixes without adding sulfur and a vulcanization accelerator. In the first mixing step, it is preferable that 0.5 to 10 parts by mass of stearic acid is further added and mixed. By adding stearic acid not in the second mixing step but in the first mixing step, the viscosity of the mixture can be lowered and the processability can be improved. In the first mixing step, additives such as carbon black, oil, wax and anti-aging agent can be further blended.

  The first mixing step can be performed using a mixer such as a Banbury mixer, a kneader, or a roll. Although the upper limit (namely, discharge temperature from a mixer) of the 1st mixing process is not specifically limited, Usually, it is preferable that it is 145-170 degreeC, More preferably, it is 155-165 degreeC.

  According to the manufacturing method according to the present embodiment, in the second mixing step (final mixing step), sulfur and a vulcanization accelerator are then added and mixed (kneaded) to the mixture obtained in the first mixing step. . The amount of each component is as described above. The second mixing step is an operation generally referred to as professional kneading. A 2nd mixing process can be performed according to a conventional method using mixers, such as an open roll and a Banbury mixer, for example, and the upper limit of mixing temperature (namely, discharge temperature from a mixer) is 70-110 degreeC, for example. It is preferable that it is 80-100 degreeC more preferably. In the second mixing step, an additive such as an antiaging agent may be further blended.

  In addition, you may perform an additional mixing process like a remill process between a 1st mixing process and a 2nd mixing process. Further, in the remilling process, additional diene rubber, filler, additive and the like can be added.

  According to this embodiment composed of the above, the hydrophobic imidazole promotes the reaction between the silica and the silane coupling agent, and exhibits a surfactant-like action by having a hydrophobic group, thereby dispersing the silica. And the balance between low heat build-up (ie, rolling resistance performance), wet grip performance and hardness (ie, steering stability) can be improved. In addition, if hydrophobic imidazole is added together with zinc white, the effect can be exhibited effectively, so adding zinc white in the first mixing step improves the dispersibility of zinc white. Thus, a decrease in general physical properties such as breaking strength can be suppressed.

  The rubber composition which concerns on embodiment obtained by the above can be used for various rubber compositions which form rubber parts, such as a pneumatic tire, vibration proof rubber, and a conveyor belt. Preferably, it is used for tires, and rubber parts of various pneumatic tires can be constituted by vulcanization molding at 140 to 180 ° C., for example, according to a conventional method. More preferably, it is used for tread rubber and / or sidewall rubber of a pneumatic tire, particularly preferably tread rubber, which reduces rolling resistance and is excellent in fuel efficiency, and is excellent in wet grip performance and driving stability. Tires can be obtained.

  Examples of the present invention will be described below, but the present invention is not limited to these examples. The raw materials used in the examples and comparative examples are as follows.

・ SBR: "SL563" manufactured by JSR Corporation
-BR: “BR150B” manufactured by Ube Industries, Ltd.
・ Silica: “Nip seal AQ” manufactured by Tosoh Silica Co., Ltd. (BET = 205 m ² / g)
Silane coupling agent: bis (3-triethoxysilylpropyl) disulfide, “Si75” manufactured by Evonik Degussa
Carbon black: N339, “Seast KH” manufactured by Tokai Carbon Co., Ltd. (N ₂ SA = 93 m ² / g)
・ Oil: “Process N140” manufactured by JX Nippon Oil & Energy Corporation
・ Wax: Nippon Seiwa Co., Ltd. “OZOACE0355”
・ Stearic acid: “Lunac S-20” manufactured by Kao Corporation
-Imidazole: manufactured by Tokyo Chemical Industry Co., Ltd.-2-methylimidazole: manufactured by Wako Pure Chemical Industries, Ltd.-2-undecylimidazole: manufactured by Wako Pure Chemical Industries, Ltd.-2-heptadecylimidazole: Wako Pure Chemical Industries, Ltd.・ 2-Phenylimidazole: Wako Pure Chemical Industries, Ltd. ・ Zinc Hana: “Zinc Hana 1” manufactured by Mitsui Kinzoku Mining Co., Ltd.
Anti-aging agent: “NOCRACK 6C” manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
・ Sulfur: “Powder sulfur” manufactured by Tsurumi Chemical Co., Ltd.
・ Vulcanization accelerator CZ: N-cyclohexyl-2-benzothiazolylsulfenamide, “Soccinol CZ” manufactured by Sumitomo Chemical Co., Ltd.
・ Vulcanization accelerator D: 1,3-diphenylguanidine, “Noxeller D” manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

  According to the composition (parts by mass) shown in Table 1 below, rubber compositions of Examples and Comparative Examples were prepared using a Banbury mixer. Specifically, first, in the first mixing step (non-pro kneading), the components described in “NP step” in Table 1 are added and mixed (discharge temperature = 160 ° C.), and then the obtained mixture is mixed with the second mixture. In the process (pro-kneading), the components described in “FN step” in Table 1 were added and mixed (discharge temperature = 90 ° C.) to prepare a tire tread rubber composition.

  About each obtained rubber composition, vulcanize | cures using a hot press on the conditions for 160 degreeC x 20 minutes, produce a test piece, hardness, rolling resistance performance, wet grip performance, and breaking strength evaluated. For Examples 2 and 5, the Mooney viscosity of the mixture after the first mixing step was measured. Each evaluation method is as follows.

Hardness: Using a type A durometer in accordance with JIS K6253, the hardness was measured at 23 ° C., and indicated as an index with the value of Comparative Example 1 being 100. The larger the value, the higher the hardness and the better the steering stability when used in a tire.

Rolling resistance performance: Using a fully automatic viscoelasticity analyzer manufactured by Ueshima Seisakusho Co., Ltd., frequency 10 Hz, initial strain 10%, measurement temperature range −40 ° C. to 100 ° C., measurement temperature step 2 ° C., dynamic strain 0.5% The tan δ value at 60 ° C. was used as an index of rolling resistance performance. The results are expressed as an index with the value of Comparative Example 1 being 100, and the smaller the value, the smaller the rolling resistance and the better.

・ Wet grip performance: Using a fully automatic viscoelasticity analyzer manufactured by Ueshima Seisakusho Co., Ltd., frequency 10 Hz, initial strain 10%, measurement temperature range −40 ° C. to 100 ° C., measurement temperature step 2 ° C., dynamic strain 0.5% The tan δ value at 0 ° C. was used as an index of wet grip performance. The results are displayed as an index with the value of Comparative Example 1 being 100, and the larger the value, the better the wet grip performance.

-Breaking strength: According to JIS K6251, the tensile test (dumbbell shape No. 3 type) was carried out to measure the tensile strength, and the value of Comparative Example 1 was represented by an index of 100. The larger the value, the greater the breaking strength and the better the reinforcement.

Mooney viscosity: The unvulcanized rubber was preheated at 100 ° C. for 1 minute and the torque value after 4 minutes was measured in Mooney units using a rotorless Mooney measuring machine manufactured by Toyo Seiki Co., Ltd. according to JIS K6300. The value was expressed as an index with the value of Example 5 taken as 100. The smaller the value, the lower the Mooney viscosity and the better the workability.

  The results are as shown in Table 1. Compared to Comparative Example 1 as a control, Comparative Example 2 in which imidazole having no substituent was added was able to improve the rolling resistance performance by 10%, but the hardness decreased. Compared to Comparative Example 2, in Comparative Example 3 in which zinc white was added in the first mixing step, although the breaking strength was improved, the effect of improving the rolling resistance performance was impaired.

  On the other hand, Comparative Example 8 to which 2-heptadecylimidazole was added had the same rolling resistance performance improving effect as Comparative Example 2 without a substituent, but the hardness was not lowered, and steering stability and rolling resistance were improved. Excellent balance between performance and wet grip performance. In contrast to Comparative Example 8, in Example 2, the breaking strength was improved while maintaining the excellent balance improvement effect of the above three performances. Example 2 is different from Comparative Example 8 in that the addition time of zinc white was changed from the second mixing step to the first mixing step, which is clearly different from Comparative Examples 2 and 3 using imidazole having no substituent. A different trend was seen. Examples 1, 3, and 4 also had excellent balance between steering stability, rolling resistance performance, and wet grip performance while maintaining break strength.

  As shown in Comparative Examples 4 to 7 and 9, as described above, the effect of the substituent was not observed in the ethyl group, undecyl group, and phenyl group.

  From the comparison between Example 2 and Example 5, by adding stearic acid in the first mixing step instead of the second mixing step, the viscosity of the mixture after the first mixing step can be reduced, and the processability It was excellent.

Claims (4)

20 to 120 parts by mass of silica, 2 to 20% by mass of a silane coupling agent based on the amount of silica, and a saturated or unsaturated hydrocarbon group having 12 or more carbon atoms is an imidazole ring with respect to 100 parts by mass of diene rubber. A first mixing step of mixing 0.2 to 3 parts by mass of a hydrophobic imidazole bonded to the 2-position of
A second mixing step of adding and mixing sulfur and a vulcanization accelerator to the mixture obtained in the first mixing step;
The manufacturing method of the rubber composition containing this.   The manufacturing method of the rubber composition of Claim 1 which further mixes a stearic acid in a said 1st mixing process.   The method for producing a rubber composition according to claim 1 or 2, wherein the hydrophobic imidazole is a 2-alkylimidazole in which an alkyl group having 15 to 19 carbon atoms is bonded to the 2-position of the imidazole ring.   It is a manufacturing method of the rubber composition for tires, The method of any one of Claims 1-3.