JP2015093969A - Rubber composition for rim cushion and pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for rim cushion exhibiting large elongation at break and excellent aging resistance, and a pneumatic tire in which the rubber composition is used as the rim cushion.SOLUTION: There is provided the rubber composition which contains a rubber composition, carbon black having an iodine adsorption amount of 70 to 130 g/kg, a vulcanization accelerator and sulfur, and in which the rubber component contains a butadiene rubber and trans-polyisoprene having a trans-bond content of 90 mol% or more, the content of the butadiene rubber in the rubber component is 30 to 70 mass%, the content of the trans-polyisoprene in the rubber component is 30 to 70 mass%, the content of the carbon black is 40 to 90 pts.mass based on 100 pts.mass of the rubber component and the mass ratio (A/S) of the content of the vulcanization accelerator (A) to the content of the sulfur (S) is 0.9 to 2.0.

Description

  The present invention relates to a rubber composition for a rim cushion and a pneumatic tire.

  A rim cushion is provided on the outer surface of the bead portion of the pneumatic tire so as to be in close contact with the rim when the tire is assembled on the wheel. Here, the rim cushion is required to have a high elongation at break from the viewpoint of detachability. In addition, when the rim cushion becomes hard due to aging, it becomes easy to be damaged due to deformation at the time of detachment or running, and therefore it is also required to have excellent aging resistance.

  For example, Patent Document 1 discloses that (A) 100 parts by weight of a diene rubber including 25 to 100 parts by weight of natural rubber and / or polyisoprene rubber and 0 to 75 parts by weight of butadiene rubber, and (B) iodine adsorption amount. 60 to 90 parts by weight of carbon black of 30 mg / g or more and less than 110 mg / g, (C) 0.5 to 10 parts by weight of an amine salt compound of a carboxylic acid-containing disulfide represented by the formula (I), (D) 1 to sulfur 4 parts by weight and (E) sulfenamide-based vulcanization accelerator 0.2 to 4 parts by weight, and the ratio (weight) of the amount of component (C) to component (E) is 4.5: A tire rubber composition satisfying the relational expression of ≧ (C) / (E) ≧ 0.2 ”is disclosed (claim 1).

JP 2008-50442 A

  Under such circumstances, the present inventor prepared and vulcanized a rubber composition containing natural rubber and / or polyisoprene, butadiene rubber, carbon black, a vulcanization accelerator and sulfur based on Patent Document 1. However, it has been clarified that the elongation at break of the obtained rubber does not necessarily satisfy the demand when a high level of performance is required for the rim cushion in the future. In addition, when the aging resistance of the obtained rubber was evaluated by an aging test (heating test), the hardness may increase significantly after the aging test. It has become clear that when requested, it does not necessarily meet that requirement.

  In view of the above circumstances, an object of the present invention is to provide a rubber composition for a rim cushion exhibiting a large elongation at break and excellent aging resistance, and a pneumatic tire using the rubber composition for the rim cushion. .

As a result of intensive studies on the above problems, the present inventors have used butadiene rubber and a specific transpolyisoprene as a rubber component, blended a specific amount of specific carbon black, and further, the content of a vulcanization accelerator and It has been found that by setting the ratio to the content of sulfur within a specific range, large breaking elongation and excellent aging resistance are exhibited, and the present invention has been achieved.
That is, the present inventors have found that the above problem can be solved by the following configuration.

(1) containing a rubber component, carbon black having an iodine adsorption amount of 70 to 130 g / kg, a vulcanization accelerator, and sulfur;
The rubber component includes butadiene rubber and trans polyisoprene having a trans bond content of 90 mol% or more, the content of the butadiene rubber in the rubber component is 30 to 70% by mass, and the rubber component The content of trans polyisoprene in is 30 to 70% by mass,
The carbon black content is 40 to 90 parts by mass with respect to 100 parts by mass of the rubber component,
A rubber composition for a rim cushion, wherein a mass ratio (A / S) of the content (A) of the vulcanization accelerator and the content (S) of sulfur is 0.9 to 2.0.
(2) A pneumatic tire using the rim cushion rubber composition described in (1) above as a rim cushion.

  As described below, according to the present invention, it is possible to provide a rubber composition for a rim cushion exhibiting a large breaking elongation and excellent aging resistance, and a pneumatic tire using the rubber composition for the rim cushion.

It is a partial section schematic diagram of the tire showing an example of the embodiment of the pneumatic tire of the present invention.

Below, the rubber composition for rim cushions of this invention and the pneumatic tire which used it for the rim cushion are demonstrated.
In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Rubber composition for rim cushion]
The rubber composition for a rim cushion of the present invention (hereinafter also referred to as the composition of the present invention) comprises a rubber component, carbon black having an iodine adsorption of 70 to 130 g / kg, a vulcanization accelerator, and sulfur. contains.
Here, the rubber component includes butadiene rubber and trans polyisoprene having a trans bond content of 90 mol% or more, and the content of the butadiene rubber in the rubber component is 30 to 70% by mass, The content of trans polyisoprene in the rubber component is 30 to 70% by mass. Moreover, content of the said carbon black is 40-90 mass parts with respect to 100 mass parts of said rubber components. The mass ratio (A / S) of the vulcanization accelerator content (A) and the sulfur content (S) is 0.9 to 2.0.
Since the composition of this invention takes such a structure, it is thought that a big breaking elongation and the outstanding aging resistance are shown.

The reason is not clear, but it is presumed that it is as follows.
As mentioned above, the composition of the present invention contains trans polyisoprene. Trans polyisoprene is known to have higher crystallinity than the cis type, but in the composition of the present invention, trans polyisoprene, butadiene rubber, and specific carbon black are blended at a predetermined ratio. Therefore, it is difficult to form microcrystals due to uneven distribution of trans polyisoprene after vulcanization. Further, the ratio between the content of the vulcanization accelerator and the content of sulfur is specific. As a result, it is considered that high breaking elongation is achieved while maintaining the initial hardness required for the rim cushion.
In addition, since the above-mentioned trans polyisoprene contained in the composition of the present invention is energetically stable, the three-dimensional network structure formed by vulcanizing the composition of the present invention is due to external energy such as heat. Small structural change. Therefore, it is considered that changes in mechanical properties such as an increase in hardness over time are suppressed, and excellent aging resistance is exhibited.

  Hereinafter, each component contained in the composition of the present invention will be described.

[Rubber component]
The rubber component contained in the composition of the present invention includes butadiene rubber and trans polyisoprene having a trans bond content of 90 mol% or more.

<Butadiene rubber>
The butadiene rubber contained in the composition of the present invention is not particularly limited as long as it is a polymer of a butadiene monomer. In addition, the thing using one type of butadiene-type monomer or the thing using two or more types of butadiene-type monomers may be used.
Examples of the butadiene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene), 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, and the like. Is mentioned. Of these, 1,3-butadiene is preferable.
The butadiene rubber is preferably a homopolymer of 1,3-butadiene.

The weight average molecular weight of the butadiene rubber is not particularly limited, but is preferably 200,000 to 3,000,000 from the viewpoint of handling.
In the present specification, the weight average molecular weight (Mw) of the rubber component is measured in terms of standard polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran as a solvent.

The content of butadiene rubber in the rubber component is 30 to 70% by mass. Especially, it is preferable that it is 40-60 mass%.
When the content of the butadiene rubber in the rubber component is less than 30% by mass, the aging resistance is lowered, and when it exceeds 70% by mass, the elongation at break becomes small and the level required for the rim cushion is not satisfied.

  The butadiene rubber does not include trans polyisoprene described later.

<Trans polyisoprene>
The trans polyisoprene contained in the composition of the present invention is a polyisoprene having a trans bond content of 90 mol% or more. Hereinafter, trans polyisoprene (polyisoprene having a trans bond content of 90 mol% or more) contained in the composition of the present invention is also simply referred to as trans polyisoprene.
Here, the trans bond content is the ratio of the trans-1,4 bond units represented by the following formula (a) among all the bond units constituting the polyisoprene. In addition, polyisoprene is usually a cis-1,4 bond unit represented by the following formula (b), a formula (c), and a trans-1,4 bond unit represented by the following formula (a). 1,2 bond units represented, and 3,4 bond units represented by the following formula (d).

  For example, when polyisoprene is composed of 99 mol of trans-1,4 bond units and 1 mol of cis-1,4 bond units, the trans bond content of polyisoprene is 99 (= 99 / (99 + 1) × 100) mol%.

  The trans bond content represents an average value. That is, when the polyisoprene is composed of one type of polyisoprene, the trans bond content represents the trans bond content of the one type of polyisoprene, and the polyisoprene has a plurality of types of polyisoprene having different trans bond contents. The trans bond content represents the mass average value of the trans bond content of each polyisoprene constituting the polyisoprene.

The content of trans polyisoprene in the rubber component is 30 to 70% by mass. Especially, it is preferable that it is 40 mass% or more from the reason which shows larger breaking elongation and more excellent aging resistance.
When the content of trans polyisoprene in the rubber component is less than 30% by mass, the elongation at break becomes small and the level required for the rim cushion is not satisfied. In addition, the aging resistance becomes insufficient. Further, when the content of trans polyisoprene in the rubber component is more than 70% by mass, the elongation at break becomes small and the level required for the rim cushion is not satisfied.

<Other rubber components>
The rubber component contained in the composition of the present invention may contain rubber components (other rubber components) other than the butadiene rubber and transpolyisoprene described above as long as the effects and objects of the present invention are not impaired.
Such “other rubber components” are not particularly limited, but specific examples thereof include natural rubber (NR), aromatic vinyl-conjugated diene copolymer rubber, acrylonitrile-butadiene copolymer rubber (NBR), and butyl rubber. (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR) and the like. The other rubber components may be used alone or in combination of two or more rubber components.
The rubber component contained in the composition of the present invention preferably contains natural rubber (NR) as the other rubber component.
Content of the other rubber component in a rubber component is 0-40 mass%, and it is preferable that it is 30 mass% or less especially.

  In the composition of the present invention, the content of trans polyisoprene is preferably 40 parts by mass or more with respect to 100 parts by mass of diene rubber other than trans polyisoprene.

〔Carbon black〕
The carbon black contained in the composition of the present invention is not particularly limited as long as the iodine adsorption amount is 70 to 130 g / kg.
The iodine adsorption amount of carbon black is preferably 110 g / kg or more because the elongation at break becomes larger.
The carbon black is preferably ISAF grade or HAF grade, and is preferably ISAF grade for the reason that the elongation at break becomes larger.
When the iodine adsorption amount of the carbon black is less than 70 g / kg, the strength required for the rim cushion is not satisfied, and when it exceeds 130 g / kg, the workability is deteriorated.
In the present specification, the iodine adsorption amount of carbon black is measured according to JIS K6217-1: 2008.

In the composition of the present invention, the content of the carbon black is 40 to 90 parts by mass with respect to 100 parts by mass of the rubber component. Especially, it is preferable that it is 50-80 mass parts.
When the carbon black content is less than 40 parts by mass with respect to 100 parts by mass of the rubber component, the strength required for the rim cushion is not satisfied. On the other hand, if the carbon black content exceeds 90 parts by mass with respect to 100 parts by mass of the rubber component, the elongation at break becomes small and the level required for the rim cushion is not satisfied.

[Vulcanization accelerator]
The vulcanization accelerator contained in the composition of the present invention is not particularly limited. Specific examples thereof include sulfenamide, thiazole, thiuram, thiourea, guanidine, dithiocarbamic acid, and aldehyde-amine. Aldehyde-ammonia-based, imidazoline-based, xanthate-based vulcanization accelerators, and the like. These may be used alone or in combination of two or more. The vulcanization accelerator is preferably a sulfenamide type.

  In the composition of the present invention, the content (A) of the vulcanization accelerator is not particularly limited as long as a mass ratio (A / S) described later is satisfied, but is 1.0% with respect to 100 parts by mass of the rubber component. It is preferable that it is -5.0 mass parts.

〔sulfur〕
The sulfur contained in the composition of the present invention is not particularly limited, and specific examples thereof include oil-treated sulfur, powdered sulfur, precipitated sulfur, highly dispersible sulfur, surface-treated sulfur, insoluble sulfur, dimorpholine disulfide, An alkylphenol disulfide etc. are mentioned, These may be used individually by 1 type and may use 2 or more types together.

  In the composition of the present invention, the sulfur content (S) is not particularly limited as long as a mass ratio (A / S) described later is satisfied, but 1.0 to 5.5 with respect to 100 parts by mass of the rubber component. It is preferably 0 parts by mass.

[A / S]
The mass ratio (A / S) of the content (A) of the vulcanization accelerator and the content (S) of sulfur is 0.9 to 2.0. Especially, it is preferable that it is 1.5 or less from the reason for improving heat aging resistance.
Here, the A / S is obtained by dividing the vulcanization accelerator content (A) by the sulfur content (S). For example, the vulcanization accelerator content (A) is the rubber. When the content is 2.5 parts by mass with respect to 100 parts by mass of the component and the sulfur content (S) is 1.5 parts by mass with respect to 100 parts by mass of the rubber component, A / S is 1.7 ( = 2.5 / 1.5).

  When the A / S is less than 0.9, the heat aging resistance is insufficient. Further, if the A / S is more than 2.0, the crack resistance is deteriorated and the level required for the rim cushion is not satisfied.

[Optional ingredients]
The composition of the present invention may further contain an additive as long as the effects and objects of the present invention are not impaired.
Examples of the additive include silica, silane coupling agent, zinc oxide (zinc white), stearic acid, anti-aging agent, processing aid, process oil, liquid polymer, terpene resin, thermosetting resin, and other than the above sulfur And various additives generally used in rubber compositions such as vulcanizing agents.

  The composition of the present invention preferably contains no silica.

[Method for producing the composition of the present invention]
The production method of the composition of the present invention is not particularly limited, and specific examples thereof include, for example, kneading the above-described components using a known method and apparatus (for example, a Banbury mixer, a kneader, a roll, etc.). The method etc. are mentioned. Especially, it is preferable to mix components other than sulfur and a vulcanization accelerator first at high temperature (preferably 140-160 degreeC), after cooling, and to mix sulfur and a vulcanization accelerator.
The composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions.

[Initial hardness]
From the viewpoint of the hardness required for the rim cushion, the initial hardness (20 ° C.) after vulcanization of the composition of the present invention is preferably 67 or more, more preferably 69 or more, and 72 or more. Is more preferable. The upper limit is not particularly limited, but is preferably 75 or less.
Here, the initial hardness is measured by press vulcanizing the composition at 160 ° C. for 20 minutes to prepare a vulcanized rubber test piece, and the vulcanized rubber test piece thus prepared is measured at 20 ° C. according to JIS K6253. Hardness (type A durometer hardness).

[Pneumatic tire]
The pneumatic tire of the present invention is a pneumatic tire using the above-described composition of the present invention for a rim cushion.
The pneumatic tire of the present invention will be described with reference to the drawings. FIG. 1 is a partial cross-sectional schematic view showing an example of an embodiment of the pneumatic tire of the present invention.

In FIG. 1, a pneumatic tire includes a pair of left and right bead portions 1 and sidewall portions 2, and a tire tread portion 3 connected to both sidewall portions 2, and a carcass in which a steel cord is embedded between the pair of left and right bead portions 1. The layer 4 is mounted, and the end portion of the carcass layer 4 is folded back from the inside to the outside around the bead core 5 and the bead filler 6 and wound up. The bead filler 6 is composed of two members, the upper part being an upper bead filler 6a and the lower part being a lower bead filler 6b.
In the tire tread portion 3, a belt layer 7 is disposed over the circumference of the tire outside the carcass layer 4. Belt cushions 8 are disposed at both ends of the belt layer 7.
An inner liner 9 is provided on the inner surface of the pneumatic tire to prevent the air filled inside the tire from leaking to the outside of the tire, and a tie rubber 10 for bonding the inner liner 9 is attached to the carcass layer 4. It is laminated between the inner liner 9.
In the bead portion 1, a rim cushion 11 is disposed at a portion in contact with the rim.
Here, the rim cushion 11 uses the above-described composition of the present invention.

  The pneumatic tire of the present invention can be manufactured, for example, according to a conventionally known method. Moreover, as gas with which a tire is filled, inert gas, such as nitrogen, argon, helium other than the air which adjusted normal or oxygen partial pressure, can be used.

  Although the tire of the present invention can be used for various vehicles such as passenger cars, as described above, it exhibits a large elongation at break and excellent aging resistance, and thus is particularly useful for trucks, buses, construction vehicles, industrial vehicles, and the like. That is, it is particularly useful as a heavy duty tire.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.

<Examples 1-4 and Comparative Examples 1-6>
The components shown in Table 1 below were blended in the proportions (parts by mass) shown in Table 1 below.
Specifically, first, among the components shown in Table 1 below, the components excluding sulfur and the vulcanization accelerator were mixed for 5 minutes using a 1.7 liter closed Banbury mixer, and reached 150 ± 5 ° C. Was released and cooled to room temperature to obtain a masterbatch. Furthermore, using the Banbury mixer, sulfur and a vulcanization accelerator were mixed with the obtained master batch to prepare rubber compositions for rim cushions (Examples 1 to 4 and Comparative Examples 1 to 6).

<Preparation of vulcanized rubber specimen>
The prepared rubber composition for a rim cushion was press vulcanized at 160 ° C. for 20 minutes to prepare a vulcanized rubber test piece.

<Evaluation of initial hardness>
About the vulcanized rubber test piece produced as described above, the hardness (type A durometer hardness) was measured at 20 ° C. according to JIS K6253, and the “initial hardness” was evaluated. The results are shown in Table 1.

<Evaluation of elongation at break>
About the vulcanized rubber test piece produced as described above, in accordance with JIS K6251: 2010, a JIS No. 3 dumbbell-type test piece (thickness 2 mm) is punched, and the elongation at break is obtained under the conditions of a temperature of 20 ° C. and a pulling speed of 500 mm / min. = Elongation at break) was measured. The results are shown in Table 1. The results were expressed as an index with Comparative Example 1 as 100. The greater the index, the greater the elongation at break.

<Evaluation of aging resistance>
An aging test (temperature: 70 ° C., time: 168 hours) is performed on the vulcanized rubber test piece prepared as described above, and the hardness (type A durometer hardness) is measured on the test piece after the aging test. Later hardness ”was evaluated. The evaluation method of hardness is the same as the initial hardness described above.
From the “initial hardness” and “the hardness after the aging test”, the aging index was calculated as follows. The results are shown in Table 1. The smaller the aging index, the smaller the increase in hardness and the better the aging resistance. Practically, the aging index is preferably 102 or less, and more preferably 101 or less. The aging index is usually 100 or more.
(Aging index) = (Hardness after aging test) × 100 / (initial hardness)

  A / S in Table 1 represents a mass ratio (A / S) between the content (A) of the vulcanization accelerator described above and the content (S) of sulfur described above.

Details of each component in Table 1 are as follows.
BR: Butadiene rubber (BR01, cis 1,4 structure: 97%, manufactured by Nippon Synthetic Rubber)
・ NR: Natural rubber (RSS # 1)
IR (A): polyisoprene (CIS-ISOPRENE SYNTHETIC RUBBER SKI-3 II GROUP, trans bond content: 4 mol%, manufactured by Nippon Synthetic Rubber Co., Ltd.)
IR (B): trans polyisoprene (TP301, trans bond content: 99 mol%, manufactured by Kuraray Co., Ltd.)
Carbon black A: HAF grade carbon black (Sheet KH, iodine adsorption amount: 90 g / kg, manufactured by Tokai Carbon Co., Ltd.)
Carbon black B: ISAF grade carbon black (show black N220, iodine adsorption amount: 119 g / kg, manufactured by Showa Cabot)
・ Carbon black C: FEF grade carbon black (seeded SO, iodine adsorption amount: 44 g / kg, manufactured by Tokai Carbon Co., Ltd.)
・ Zinc oxide: 3 types of zinc oxide (manufactured by Shodo Chemical Industry Co., Ltd.)
・ Stearic acid: Stearic acid YR (manufactured by NOF Corporation)
Antiaging agent: Santoflex 6PPD (manufactured by Solutia Europe)
・ Process oil: Extract No. 4 S (made by Showa Shell Sekiyu KK)
・ Vulcanization accelerator: Noxeller NS (made by Ouchi Shinsei Chemical Co., Ltd.)
・ Sulfur: Oil-treated sulfur (manufactured by Karuizawa Refinery)

As can be seen from Table 1, as compared with Comparative Example 1 containing no trans polyisoprene, Examples 1 to 4 containing trans polyisoprene all showed large elongation at break and excellent aging resistance.
From the comparison of Examples 1 to 3, Example 3 in which the iodine adsorption amount of carbon black was 110 g / kg or more showed a larger elongation at break.
From a comparison between Examples 1 and 2, Example 2 in which the content of transpolyisoprene in the rubber component was 40% by mass or more showed larger breaking elongation and better aging resistance.
From a comparison between Examples 2 and 4, Example 2 in which A / S was 1.5 or less had a higher initial hardness and was more suitable for a rim cushion.

Comparative Example 3 using polyisoprene having a trans bond content less than a specific value was insufficient in aging resistance.
Further, Comparative Example 4 using carbon black having an iodine adsorption amount less than a specific value had a small elongation at break and an insufficient aging resistance.
Further, Comparative Example 5, which contains trans polyisoprene but the content of trans polyisoprene in the rubber component is less than 30% by mass, has a small elongation at break and has insufficient aging resistance.
In Comparative Example 6 containing trans polyisoprene, the trans polyisoprene content in the rubber component exceeds 70% by mass, and the butadiene rubber content in the rubber component is less than 30% by mass. And the aging resistance was insufficient.

DESCRIPTION OF SYMBOLS 1 Bead part 2 Side wall part 3 Tire tread part 4 Carcass layer 5 Bead core 6 Bead filler 6a Upper bead filler 6b Lower bead filler 7 Belt layer 8 Belt cushion 9 Inner liner 10 Thai rubber 11 Rim cushion

Claims (2)

Containing a rubber component, carbon black having an iodine adsorption of 70 to 130 g / kg, a vulcanization accelerator, and sulfur;
The rubber component includes butadiene rubber and trans polyisoprene having a trans bond content of 90 mol% or more, and the content of the butadiene rubber in the rubber component is 30 to 70 mass%, and the rubber component The content of trans polyisoprene in is 30 to 70% by mass,
The content of the carbon black is 40 to 90 parts by mass with respect to 100 parts by mass of the rubber component,
A rubber composition for a rim cushion, wherein a mass ratio (A / S) of the content (A) of the vulcanization accelerator and the content (S) of sulfur is 0.9 to 2.0.   A pneumatic tire using the rubber composition for a rim cushion according to claim 1 as a rim cushion.