JP6320884B2 - Rubber composition and pneumatic tire - Google Patents

Description

  The present invention relates to a rubber composition and a pneumatic tire using the same.

  Conventionally, silica is blended as a filler in order to improve the low exothermic property (less likely to generate heat) of a rubber composition. Since silica easily aggregates in a rubber composition, it is known that a modified liquid polymer modified with an alkoxysilyl group is blended with silica in order to improve the dispersibility of the silica.

  For example, Patent Document 1 discloses that a liquid styrene-butadiene rubber having a number average molecular weight of 2,000 to 50,000 displaced by an alkoxysilyl group is blended with a silica-blended rubber composition. Patent Document 2 discloses that a liquid polybutadiene having a number average molecular weight of 500 to 10,000 having an alkoxysilyl group is blended with a rubber component mainly composed of styrene butadiene rubber together with silica and a silane coupling agent. In Patent Document 3, a modified diene rubber modified with an organosilicon compound having an alkoxy group is blended with a low molecular weight diene rubber having a weight average molecular weight of 500 to 10,000 as a modifier in a rubber composition containing silica. Is disclosed. Patent Document 4 discloses that liquid polybutadiene having an alkoxysilyl group introduced through a urethane bond at the terminal is blended with a rubber composition containing silica.

  Conventionally, the modified liquid polymer modified with an alkoxysilyl group is used in a rubber composition containing silica. This is for improving the dispersibility of the silica by reacting the siloxyl group on the silica surface which causes aggregation with the alkoxysilyl group of the modified liquid polymer. Since such an effect cannot be expected in a rubber composition containing carbon black that does not contain silica, it has not been considered to use a modified liquid polymer modified with an alkoxysilyl group in such a rubber composition containing carbon black. .

JP 2005-146115 A JP 2006-063209 A JP 2002-114874 A JP 2005-350603 A

  As described above, silica is used for the purpose of improving low heat build-up, but generally there is a problem that silica has lower reinforcement than carbon black. Therefore, it is required to improve the low heat buildup in the rubber composition containing carbon black.

  An object of the present invention is to improve low heat buildup in a rubber composition containing carbon black.

The rubber composition according to the present invention comprises 100 parts by mass of a solid diene rubber, 10 to 150 parts by mass of carbon black, and 1 to 1 modified liquid polybutadiene and / or modified liquid polyisoprene having a modified group containing an alkoxysilyl group. It contains 20 parts by mass and does not contain silica. The pneumatic tire according to the present invention is formed using the rubber composition.

  According to the present invention, in a rubber composition containing carbon black, by blending a modified liquid polybutadiene having an alkoxysilyl group and / or a modified liquid polyisoprene, there is little change in physical properties over time, and low heat build-up and reinforcement are achieved. An excellent rubber composition can be provided.

  The present inventor accidentally blended an alkoxysilyl group-modified liquid polymer, which was conventionally considered effective only in a silica-blended rubber composition, into a carbon black-blended rubber composition containing no silica. Surprisingly, it has been found that the low exothermicity is improved. In general, when a liquid polymer is added to a rubber composition, the reinforcing property tends to decrease. However, the modified liquid polybutadiene or modified liquid polyisoprene having an alkoxysilyl group has an advantageous effect that the reinforcing property is improved. was gotten. The present invention has been made based on such findings.

  The rubber composition according to the present embodiment is a rubber composition in which a reinforcing filler consisting only of carbon black (B) is blended with a diene rubber (A) as a rubber component. The modified liquid polybutadiene and / or modified liquid polyisoprene (C) is blended.

  The diene rubber as the rubber component (A) 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 and the like can be mentioned, and these can be used alone or in admixture of two or more. More preferably, it is NR, SBR, BR, or a blend rubber of two or more thereof. The diene rubber (A) is made of a solid rubber that does not have fluidity at room temperature (23 ° C.), and the modified liquid polybutadiene / polyisoprene of (C) is a diene rubber (A). Is not included. The number average molecular weight (Mn) of the diene rubber (A) is usually 100,000 or more, and Mn may be 100,000 to 1,200,000 as one embodiment. In this specification, a number average molecular weight is a value (polystyrene conversion value) measured at 40 ° C. by GPC (gel permeation chromatography), solvent: THF (tetrohydrofuran).

The carbon black (B) is not particularly limited, and various known varieties can be used. For example, when used for tire tread rubber, those having a nitrogen adsorption specific surface area (N ₂ SA) (JIS K6217-2) of 40 to 150 m ² / g are preferably used. Specifically, SAF class (N100 series), ISAF class (N200 series), HAF class (N300 series), and FEF class (N500 series) (both ASTM grade) are preferably used. The nitrogen adsorption specific surface area is more preferably 70 to 150 m ² / g.

  The blending amount of carbon black is appropriately set so as to obtain the reinforcing properties required depending on the application, and is usually 10 to 150 parts by mass with respect to 100 parts by mass of the diene rubber (A), 30 to 30 120 mass parts may be sufficient and 40-100 mass parts may be sufficient.

  The rubber composition according to this embodiment does not contain silica. That is, the reinforcing filler consists of carbon black only, and silica is not blended as the reinforcing filler. This is because when silica is blended, the reinforcing property is lowered.

  The (C) modified liquid polybutadiene and / or modified liquid polyisoprene (hereinafter, both may be collectively referred to as a modified liquid polymer) is a liquid polymer having fluidity at room temperature (23 ° C.). In order to have fluidity at room temperature, the number average molecular weight (Mn) of the modified liquid polymer is preferably 1000 to 50000, more preferably 1000 to 15000.

  The modified liquid polymer (C) may be modified liquid polybutadiene, modified liquid polyisoprene, or a combination of both. As described above, when the diene polymer chain constituting the main chain of the modified liquid polymer is polybutadiene / polyisoprene, changes in physical properties with time can be reduced. For example, in the case of a liquid styrene-butadiene copolymer, since a styrene unit having no double bond is contained, the crosslinking efficiency is low, and the physical property change is large because it easily shifts to a peripheral member. On the other hand, liquid polybutadiene and liquid polyisoprene have a higher crosslinking efficiency than liquid styrene butadiene copolymers, and therefore, there is no transition to peripheral members, and changes in physical properties over time can be reduced.

  The modified liquid polymer (C) has a modified group containing an alkoxysilyl group. Such a modifying group may be introduced at the end (both ends or one end) of the molecular chain of the main chain, or may be introduced at one or a plurality of positions in the molecular chain. In a preferred embodiment, the modifying group may be introduced at both ends of the molecular chain. The alkoxysilyl group is preferably an alkyl dialkoxysilyl group or a trialkoxysilyl group, more preferably a trialkoxysilyl group such as a triethoxysilyl group or a trimethoxysilyl group.

  The modifying group of the modified liquid polymer (C) may further contain an aromatic ring. By including an aromatic ring together with the alkoxysilyl group at the modified site, the above-described effects such as low exothermic property and excellent reinforcement can be enhanced. Examples of the aromatic ring include a benzene ring and a condensed benzene ring (for example, naphthalene ring, pyrene ring).

  The modified liquid polymer (C) having a modified group containing an alkoxysilyl group is a commercially available liquid polybutadiene or liquid polyisoprene having a hydroxyl group, a carboxyl group, an acid anhydride group or the like (hereinafter, both are collectively referred to as a liquid diene polymer). Can be synthesized from For example, (i) an alkoxysilyl group can be introduced through a urethane bond by reacting a liquid diene polymer having a hydroxyl group with a silane compound having an isocyanate group and an alkoxy group. (Ii) A liquid diene polymer having a hydroxyl group is reacted with a diisocyanate compound to introduce an isocyanate group via a urethane bond, and then reacted with a silane compound having an amino group and an alkoxy group. An alkoxysilyl group can be introduced through a bond and a urea bond. (Iii) An alkoxysilyl group can be introduced through an amide bond by reacting a liquid diene-based polymer having a carbosyl group with a silane compound having an isocyanate group and an alkoxy group. (Iv) By reacting a liquid diene polymer having an acid anhydride group with a silane compound having an isocyanate group and an alkoxy group, an alkoxysilyl group can be introduced via an imide bond.

  In order to introduce an aromatic ring into the modifying group, for example, in (ii) above, an aromatic diisocyanate compound may be used as the diisocyanate compound. Examples of the aromatic diisocyanate compound include phenylene diisocyanate, tolylene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI), 2,4′-diphenylmethane diisocyanate, and naphthalene diisocyanate. Nart, xylylene diisocyanate and the like. In this case, the modifying group is represented by the following general formula (1). The modifying group may be directly bonded to the main chain diene polymer chain, or may be bonded via any linking group.

式中、Ｒ¹、Ｒ²及びＲ³は、それぞれ炭素数１〜６のアルキル基又は炭素数１〜６のアルコキシ基を表し、少なくとも１つはアルコキシ基である。好ましくは、炭素数１〜３のアルキル基又はアルコキシ基である。アルキル基としては、例えば、メチル基又はエチル基が好ましい。アルコキシ基としては、例えば、メトキシ基又はエトキシ基が好ましい。Ｒ¹、Ｒ²及びＲ³は、好ましくは２つ以上がアルコキシ基であり、更に好ましくは３つともアルコキシ基である。

In the formula, R ¹ , R ² and R ³ each represent an alkyl group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6 carbon atoms, and at least one is an alkoxy group. Preferably, it is a C1-C3 alkyl group or an alkoxy group. As the alkyl group, for example, a methyl group or an ethyl group is preferable. As the alkoxy group, for example, a methoxy group or an ethoxy group is preferable. Two or more of R ¹ , R ² and R ³ are preferably alkoxy groups, and more preferably all three are alkoxy groups.

X represents a C1-C18 divalent hydrocarbon group which may contain a hetero atom. Examples of the hetero atom include at least one selected from an oxygen atom, a nitrogen atom, a halogen atom, and a sulfur atom. X preferably represents an alkylene group having 1 to 18 carbon atoms (more preferably 1 to 6 carbon atoms) (that is, an alkanediyl group), and may be linear or branched. In one embodiment, X is a linear alkylene group represented by — (CH ₂ ) _n —, where n is an integer of 1 to 6 (preferably an integer of n = 1 to 3).

R ⁴ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or a methyl group, and still more preferably a hydrogen atom.

  Z is a C6-C20 divalent hydrocarbon group containing an aromatic ring (for example, a benzene ring, a naphthalene ring, a pyrene ring, etc.), for example, an arylene group such as a phenylene group, a tolylene group, a naphthylene group, Examples thereof include aryldialkylene groups such as xylylene groups, and bisarylene groups such as methylenediphenyl groups that are residues of the above MDI.

  The modified liquid polymers (C) listed above may be used alone or in combination of two or more. The compounding amount of the modified liquid polymer (C) is preferably 1 to 20 parts by mass with respect to 100 parts by mass of the diene rubber (A). By blending 1 part by mass or more, the effect of improving low heat buildup can be enhanced. Moreover, the fall of reinforcement can be suppressed because a compounding quantity is 20 mass parts or less. The blending amount of the modified liquid polymer (C) is more preferably 3 to 18 parts by mass, still more preferably 5 to 15 parts by mass.

  In the rubber composition according to the present embodiment, in addition to the above-described components, various types of rubber compositions generally used in rubber compositions such as zinc white, stearic acid, anti-aging agent, wax, vulcanizing agent, and vulcanization accelerator. Additives can be blended. Examples of the vulcanizing agent include sulfur components such as powdered sulfur, precipitated sulfur, colloidal sulfur, insoluble sulfur, and highly dispersible sulfur. Although not particularly limited, the blending amount thereof is 100 parts by mass of diene rubber. It is preferable that it is 0.1-10 mass parts with respect to it, More preferably, it is 0.5-5 mass parts.

  The rubber composition according to the embodiment can be prepared by kneading according to a conventional method using a commonly used Banbury mixer, kneader, roll, or other mixer. That is, in the first mixing stage, carbon black and the modified liquid polymer are added to the diene rubber together with other additives excluding the vulcanizing agent and the vulcanization accelerator, and then the resultant mixture is finally mixed. A rubber composition can be prepared by adding and mixing a vulcanizing agent and a vulcanization accelerator in the mixing stage.

  The rubber composition thus obtained can be used for various rubber members for tires, vibration-proof rubbers, conveyor belts and the like. Preferably, it is used for tires, and can be applied to various parts of tires such as tread rubber and sidewall rubber of pneumatic tires of various sizes such as for passenger cars and heavy loads of trucks and buses. According to a conventional method, the rubber composition is molded into a predetermined shape by, for example, extrusion, and combined with other components, and then vulcanized at, for example, 140 to 180 ° C. to produce a pneumatic tire. it can. Among these, it is preferably used for a tread rubber of a tire, and more preferably used for a tread rubber of a heavy-duty pneumatic tire requiring high reinforcement.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  Using a Banbury mixer, according to the formulation (parts by mass) shown in Table 1 below, first, in the first mixing stage, other compounding agents except for sulfur and vulcanization accelerator are added to the diene rubber component and kneaded ( (Discharge temperature = 160 ° C.) Then, sulfur and a vulcanization accelerator were added and kneaded to the obtained kneaded product in the final mixing stage (discharge temperature = 90 ° C.) to prepare a rubber composition. The details of each component in Table 1 are as follows.

・ NR: RSS3 ・ BR: “BR150B” manufactured by Ube Industries, Ltd.
・ Carbon black: “Seast 3” manufactured by Tokai Carbon Co., Ltd.
・ Silica: “Ultrasil VN3” manufactured by Evonik Degussa
Silane coupling agent: “Si69” manufactured by Evonik Degussa
・ Zinc flower: "Zinc flower 3" manufactured by Mitsui Mining & Smelting Co., Ltd.
・ Stearic acid: “Lunac S20” manufactured by Kao Corporation
Anti-aging agent: “NOCRACK 6C” manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
・ Sulfur: “Sulfur Powder” manufactured by Tsurumi Chemical Co., Ltd.
・ Vulcanization accelerator: “Soxinol CZ” manufactured by Sumitomo Chemical Co., Ltd.
-Liquid BR: unmodified liquid polybutadiene, Mn = 8000, Kuraray "LBR-307"
-Liquid IR: Unmodified liquid polyisoprene, Mn = 28000, "LIR-30" manufactured by Kuraray
Liquid SBR: Unmodified liquid styrene butadiene copolymer, Mn = 3200, “Ricon 181” manufactured by Clay Valley
OH-modified liquid BR: hydroxyl-terminated liquid polybutadiene having hydroxyl groups at both ends, Mn = 2800, “R-45HT” manufactured by Idemitsu Kosan Co., Ltd.
OH-modified liquid IR: hydroxyl-terminated liquid polyisoprene having hydroxyl groups at both ends, Mn = 2500, “Poly-ip” manufactured by Idemitsu Kosan Co., Ltd.

  Silyl-modified liquid BR: 100 g of hydroxyl-terminated liquid polybutadiene having hydroxyl groups at both ends (“R-45HT”, Mn = 2800, manufactured by Idemitsu Kosan Co., Ltd.) and 4,4′-diphenylmethane diisocyanate (MDI, Sumika) 19 g of “Sumijour 44S” manufactured by Bayer Urethane Co., Ltd. was placed in a container and reacted at 70 ° C. for 2 hours while stirring. As a result, the hydroxyl groups at both ends of the liquid polybutadiene reacted with the isocyanate groups of MDI, and the isocyanate groups were introduced via urethane bonds. Subsequently, 17 g of 3-aminopropyltriethoxysilane (“KBE-903” manufactured by Shin-Etsu Chemical Co., Ltd.) was added and reacted at 70 ° C. for 2 hours. As a result, the isocyanate group at both ends and the amino group of aminosilane reacted to obtain liquid polybutadiene (silyl-modified liquid BR) in which alkoxysilyl groups were introduced at both ends via urea bonds.

  Silyl-modified liquid IR: 100 g of hydroxyl-terminated liquid polybutadiene having hydroxyl groups at both ends (“Poly-ip” manufactured by Idemitsu Kosan Co., Ltd., Mn = 2500) and 4,4′-diphenylmethane diisocyanate (MDI, Sumika) 20 g of “Sumidur 44S” manufactured by Bayer Urethane Co., Ltd. was placed in a container and allowed to react for 2 hours at 70 ° C. with stirring, whereby the hydroxyl groups at both ends of the liquid polybutadiene and the isocyanate group of MDI reacted, An isocyanate group was introduced through a urethane bond, and then 18 g of 3-aminopropyltriethoxysilane (“KBE-903” manufactured by Shin-Etsu Chemical Co., Ltd.) was added and reacted at 70 ° C. for 2 hours. As a result, the isocyanate group at both ends reacts with the amino group of aminosilane, and the alkoxysilyl group is converted via a urea bond. Liquid polyisoprene which has been introduced into the terminal (silyl-modified liquid IR) were obtained.

  About each obtained rubber composition, the test piece of the predetermined shape vulcanized | cured for 30 minutes at 160 degreeC was evaluated for the time change of low heat build-up property, reinforcement property, and a physical property. Each evaluation method is as follows.

  Low exothermic property: According to JIS K6394, the loss factor tan δ was measured under the conditions of a frequency of 10 Hz, a static strain of 10%, a dynamic strain of ± 1%, and a temperature of 70 ° C. . The lower the value, the less heat is generated and the better the low heat generation.

  -Reinforcing property: According to JIS K6251, a tensile test (dumbbell shape No. 3) was carried out, the tensile strength at 100% elongation was measured, and the value of Comparative Example 1 was expressed as an index. The larger the value, the greater the elasticity and the better the reinforcement.

  ・ Changes in physical properties over time: After storing a vulcanized rubber piece prepared in a length of 40 mm, a width of 40 mm, and a height of 30 mm in an oven at 40 ° C. for 20 days, the rubber hardness (surface hardness) at the center of the surface is high. The rubber hardness (internal hardness) at the center of the cut surface at a position of 15 mm was measured at 23 ° C. using a type A durometer in accordance with JIS K6253. The obtained numerical value was applied to the following equation to evaluate the change in physical properties. The closer the value is to 100, the smaller the physical property changes with time and the better. (Formula): Physical property change = (Surface hardness / Internal hardness) × 100

  The results are as shown in Table 1. In Comparative Example 2 in which half of the carbon black was replaced with silica, compared to Comparative Example 1 as a control, the low exothermic property was improved, but the reinforcement was reduced. Further, in Comparative Examples 3 to 5 to which the unmodified liquid diene polymer was added, the reinforcing property was lower than that of Comparative Example 1. In particular, in Comparative Example 5 in which liquid SBR was added, the change in physical properties with time was also large. Further, in Comparative Examples 6 and 7 to which OH-modified liquid BR / IR was added, a decrease in reinforcing property was observed as in the case of using an unmodified liquid polymer. On the other hand, in Examples 1 to 4 in which modified liquid BR / IR modified with alkoxysilyl groups was added, unmodified or hydroxyl-modified liquid diene polymer was also added to Comparative Example 1 as a control. Also in Comparative Examples 3 to 7, the low heat build-up was improved and the reinforcement was also improved. Moreover, the time change of the physical property was few compared with the comparative example 5 which added liquid SBR.

Claims (4)

100 parts by weight of solid diene rubber, 10 to 150 parts by weight of carbon black, 1 to 20 parts by weight of modified liquid polybutadiene and / or modified liquid polyisoprene having a modified group containing an alkoxysilyl group, and silica Rubber composition not containing.   The rubber composition according to claim 1, wherein the modified group of the modified liquid polybutadiene and / or modified liquid polyisoprene contains an aromatic ring.   A pneumatic tire comprising the rubber composition according to claim 1.   The pneumatic tire according to claim 3, further comprising a tread rubber made of the rubber composition.