JP2005139352A - Rubber composition for tread part of pneumatic tire for emergency and pneumatic tire for emergency using the rubber composition in its tread part - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a rubber composition for a tread part of a pneumatic tire for emergency having both good ozone crack resistance and grip performance. <P>SOLUTION: The rubber composition comprises 100 pts.wt. rubber component comprising (a) 55-83 pts.wt. solution-polymerized styrene-butadiene copolymer rubber (SBR) comprising 30-45 wt.% styrene and 20-50 wt.% vinyl originated from butadiene and (b) 45-17 pts.wt. polybutadiene rubber (BR). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rubber composition for a tread portion of an emergency pneumatic tire. More specifically, the present invention relates to a rubber composition for a tread portion of an emergency pneumatic tire that has good ozone crack resistance and grip performance. The present invention also relates to an emergency pneumatic tire in which the above rubber composition is used in a tread portion.

  Emergency pneumatic tires installed in passenger cars, minivans, etc., have often been stored in trunks, but nowadays they are often installed outside the vehicle for the purpose of securing the interior space. For this reason, ozone crack resistance is also regarded as important in emergency pneumatic tires.

  On the other hand, the emergency pneumatic tire itself is also stored for the purpose of temporary use when the standard tire used in normal driving becomes unusable due to a failure such as puncture. Unlike so-called “ground tires”, which are standard tires mounted on vehicles for the purpose of reducing space and weight, they are generally narrower, thinner, and relatively simple in structure. "Emergency pneumatic tires" are being used.

  In the T type emergency pneumatic tire having the structural features as described above, a higher air pressure is used compared to the ground tire in order to support a load equivalent to that of the ground tire. Also, there is a stricter tire than the ground tire, and since the width is narrow, higher grip performance is required from the viewpoint of ensuring steering stability.

  However, in the prior art relating to emergency pneumatic tires, for example, emergency pneumatic tires aiming to achieve both weight reduction and durability and / or handling stability, or to improve productivity and prevent manufacturing failures. Although the above structural improvements have been made, it is the actual situation that no remarkable effect is found in both the above-described ozone crack resistance and steering stability.

  Prior art document information related to the invention of this application includes the following.

JP 2002-205509 A JP 2001-80317 A JP 2000-43505 A Japanese Patent Laid-Open No. 8-58312 JP-A-7-188466 JP-A-6-247104 JP-A-5-339424 Japanese Patent Laid-Open No. 5-319012

Japanese Patent Laid-Open No. 5-319001 JP-A-5-162506 Japanese Patent Laid-Open No. 5-603 Japanese Patent Laid-Open No. 3-176204 Japanese Utility Model Publication No. 1-150104 JP-A-1-289702 JP-A-1-95906 JP 63-306904 A

  As described above, in the technical field, there is an increasing demand for an emergency pneumatic tire having both good ozone crack resistance and steering stability. Accordingly, an object of the present invention is to provide a rubber composition for a tread portion of an emergency pneumatic tire having both good ozone crack resistance and grip performance.

The above purpose is
(A) 55-83 parts by weight of a solution polymerized styrene-butadiene copolymer rubber (SBR) comprising vinyl derived from 30-45% by weight styrene and 20-50% by weight butadiene;
(B) 45 to 17 parts by weight of polybutadiene rubber (BR);
The rubber composition for a tread part of an emergency pneumatic tire comprising 100 parts by weight of a rubber component.

  By carrying out the present invention, there is provided a rubber composition for a tread portion of an emergency pneumatic tire having both good ozone crack resistance and grip performance. Such a rubber composition is suitable for use in the tread portion of an emergency pneumatic tire having both good ozone crack resistance that can withstand long-term storage outside the vehicle and good steering stability.

  In the present invention, a specific solution-polymerized styrene-butadiene copolymer rubber (SBR) and a polybutadiene rubber (BR) defined by a styrene content and a vinyl content are blended at a specific ratio, thereby long-term storage at a low temperature. This is based on the finding that it is possible to provide a rubber composition for a tread of an emergency pneumatic tire that can achieve both ozone crack resistance and handling stability at a high level.

That is, the rubber composition for a tread of an emergency pneumatic tire according to the present invention is:
(A) 55-83 parts by weight of a solution polymerized styrene-butadiene copolymer rubber (SBR) comprising vinyl derived from 30-45% by weight styrene and 20-50% by weight butadiene;
(B) 45 to 17 parts by weight of polybutadiene rubber (BR);
A rubber composition for a tread portion of an emergency pneumatic tire, comprising 100 parts by weight of a rubber component.

  The styrene content of the solution-polymerized styrene-butadiene copolymer rubber (SBR) used in the rubber composition for a tread of an emergency pneumatic tire according to the present invention is 30 to 45% by weight, preferably 33 to 42% by weight. It is. When the styrene content is less than 30% by weight, the grip performance in the rubber composition after vulcanization is lowered, and when such a rubber composition is used in the tread portion, the steering stability as a tire is lowered. It is not preferable. Conversely, when the styrene content exceeds 45% by weight, high grip performance is obtained, but ozone crack resistance, particularly ozone crack resistance at low temperatures, is not preferable.

  Further, the content of vinyl derived from butadiene in the solution-polymerized styrene-butadiene copolymer rubber (SBR) used in the rubber composition for a tread of an emergency pneumatic tire according to the present invention is 20 to 50% by weight, Preferably it is 25 to 45% by weight. A vinyl content of less than 20% by weight is not preferable because sufficient grip performance cannot be obtained. Conversely, when the vinyl content exceeds 50% by weight, ozone crack resistance in the rubber composition after vulcanization is lowered, which is not preferable.

  Further, the rubber component used in the rubber composition for a tread of an emergency pneumatic tire according to the present invention contains 55 to 83 of the above-mentioned solution-polymerized styrene-butadiene copolymer rubber (SBR) per 100 parts by weight. Parts by weight, preferably 60-80 parts by weight, and polybutadiene rubber (BR), 45-17 parts by weight, preferably 40-20 parts by weight.

  When the blending amount of the solution polymerized styrene-butadiene copolymer rubber (SBR) is less than 55 parts by weight with respect to 100 parts by weight of the rubber component (that is, the blending amount of the polybutadiene rubber (BR) is 100 parts by weight of the rubber component) On the other hand, when it exceeds 45 parts by weight, the grip performance of the rubber composition after vulcanization is lowered, and when such a rubber composition is used in the tread part, the handling stability as a tire is lowered, which is not preferable.

  Conversely, when the amount of the solution polymerized styrene-butadiene copolymer rubber (SBR) exceeds 83 parts by weight with respect to 100 parts by weight of the rubber component (that is, the amount of polybutadiene rubber (BR) is 100 parts by weight of the rubber component). In the case where it is less than 17 parts by weight with respect to the part), the ozone crack resistance of the rubber composition after vulcanization is reduced. Since durability as a tire when exposed is lowered, it is not preferable.

  The polybutadiene rubber (BR) used in the rubber component of the rubber composition for a tread of an emergency pneumatic tire according to the present invention is any one commonly used for a rubber composition for a tire tread in the technical field. However, polybutadiene rubber having a cis bond content of 90 mol% or more is preferable.

  A vulcanizing agent such as sulfur is also blended in the rubber composition for a tread of an emergency pneumatic tire according to the present invention. When sulfur is used as the vulcanizing agent, for example, powder sulfur or the like, which is well known in the rubber compounding technical field, can be used. It can be a general blending amount.

  The rubber composition for a tread of an emergency pneumatic tire according to the present invention includes a filler (carbon black, silica, etc.), a plasticizer, a softener, a vulcanization aid, a vulcanization accelerator, and a vulcanization retarder. , A vulcanization activator, an anti-aging agent, etc., and / or other various additives generally used in the field of rubber compounding technology. The blending amount of these additives can also be a conventional general blending amount as long as the object of the present invention is not violated.

  Furthermore, the rubber composition for a tread of an emergency pneumatic tire according to the present invention is produced by mixing the above-described components using a known rubber kneading machine (for example, a roll, a Banbury mixer, a kneader, etc.). can do.

  In a preferred embodiment of the present invention, the above-mentioned rubber composition has a loss tangent (tan δ) measured at 0 ° C. after vulcanization of 0.48 or more, preferably 0.50 or more. When the loss tangent (tan δ) is less than 0.48, the grip performance of the rubber composition after vulcanization is lowered, and when such a rubber composition is used in the tread portion, the steering stability as a tire is lowered. This is not preferable.

  In its further preferred embodiment, the present invention also contemplates the use of the rubber composition according to the present invention in the tread portion of an emergency pneumatic tire. That is, by using a rubber composition that satisfies the above-described requirements in the tread portion, an emergency pneumatic tire is provided that can achieve both high levels of ozone crack resistance and handling stability during long-term storage at low temperatures. The

  The present invention will be described in more detail with reference to the following standard examples, comparative examples, and examples. However, the technical scope of the present invention is not limited to these examples.

Standard A, Comparative Examples A-1 to A-3, and Examples A-1 and A-2
Ingredients various rubber compositions and further details of various rubber constituting the rubber component used in the preparation of various test pieces which will be described later, are listed in the following table I. As described in Table I, the various styrene-butadiene copolymer rubbers (SBR) used here are oil-extracted with 37.5 parts by weight of the oil component per 100 parts by weight of the rubber component. (That is, the content of the oil component = about 27.3 wt%). Among these, the solution-polymerized styrene-butadiene copolymer rubber (SBR) according to the present invention is SBR4 and SBR6.

  Various compounding components other than the rubber components used in the preparation of various rubber compositions and various test pieces described below are listed below.

Carbon black (CB): “Seast KH” (HAF grade) manufactured by Tokai Carbon Co., Ltd.
Anti-aging agent (6PPD): “SANTOFLEX 13” (N-phenyl-N′-1,3-dimethylbutyl-p-phenylenediamine) manufactured by FLEXSYS
Wax: “Sunnock” manufactured by Ouchi Shinsei Chemical Co., Ltd.
Stearic acid: “Bead stearic acid” manufactured by NOF Corporation
Zinc Hana: “Zinc oxide 3 types” manufactured by Shodo Chemical Industry Co., Ltd.
Aroma oil: “Flex M” manufactured by Fuji Kosan Co., Ltd.
Vulcanization accelerator (CBS): “Noxeller CZ-G” (N-cyclohexyl-2-benzothiazolesulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.
Sulfur: “Oil-treated sulfur” (4.76% oil-treated powdered sulfur) manufactured by Karuizawa Refinery

Preparation of various rubber compositions and various test pieces The components other than sulfur and vulcanization accelerator (CBS) shown in Table II below were mixed in a 1.8 L hermetic Banbury mixer in the compounding amounts shown in Table II below. Mixing and kneading for ˜5 minutes, the master batch was released when the temperature reached 160 ± 5 ° C. To this master batch, sulfur and a vulcanization accelerator (CBS) having the blending amounts shown in Table II below were added and kneaded with an 8-inch open roll, and Standard Example A and Comparative Examples A-1 to A-3. The rubber compositions of Examples A-1 and A-2 were obtained. Next, various rubber compositions were press vulcanized at 160 ° C. for 20 minutes in a 15 cm × 15 cm × 0.2 cm mold to prepare various target test pieces.

  However, as described above, the compounding amounts of various styrene-butadiene copolymer rubbers (SBR) described in Table II below and Table III below are all 37.5% with respect to 100 parts by weight of the rubber component. Since the oil component of parts by weight is contained as an oil fraction (that is, the content of the oil component = about 27.3 wt%), the amount of the true rubber component and the amount of the oil component in various rubber compositions As for (including the blending amount of aroma oil), it is necessary to consider this oil extended oil component.

Measurement of physical properties of various test pieces Various physical properties of the various test pieces were measured according to the following test methods.

1) Ozone crack resistance:
With respect to the above various test pieces, the strain rate [%] at which cracks were generated was measured at an ozone concentration of 50 pphm and a temperature of 0 ° C. in accordance with JIS K6259 (former K6301). It means that the larger the strain rate [%], the higher the ozone crack resistance of the vulcanized rubber composition.

2) Loss tangent (tan δ):
For each of the above test pieces, the loss tangent (tan δ) is measured using a viscoelastic spectrometer under the conditions of a frequency of 20 Hz, a static strain of 10%, a dynamic strain of ± 2%, and a temperature of 0 ° C. in accordance with JIS K6394. did. A larger loss tangent (tan δ) means higher grip performance of the rubber composition after vulcanization.

Evaluation of Physical Properties of Various Test Pieces The results of various physical property measurements of 1) and 2) for the above various test pieces are also shown in Table II. In addition, as shown in Table II above, in all examples, all the formulations except the composition of the rubber component and the blending amount of the aroma oil are the same, and the total blending of the oil component including the above aroma oil The amount was also adjusted to be the same in all examples (about 50 parts by weight with respect to 100 parts by weight of the rubber component).

  The rubber composition of standard example A is an emulsion-polymerized styrene-butadiene copolymer rubber generally used in a tire tread rubber composition with respect to 100 parts by weight of a rubber component (excluding an oil-extended oil component). A control standard having a standard composition as a rubber composition for a tire tread, comprising 60 parts by weight of (SBR1) (excluding oil-extended oil components) and 40 parts by weight of a high cis type polybutadiene rubber (BR) It is the rubber composition which becomes. The strain rate measured in the above-mentioned 1) ozone crack resistance test was 30%, and the value of loss tangent (tan δ) serving as an index of grip performance was 0.377. In the evaluation of various physical properties of various comparative examples and examples described below, the test piece of the standard example A is used as a reference.

  The rubber composition of Comparative Example A-1 was the same as that of Standard Example A except that the emulsion-polymerized styrene-butadiene copolymer rubber (SBR1) was replaced with a comparative solution-polymerized styrene-butadiene copolymer rubber (SBR2). It is a comparative rubber composition having the same composition as the rubber composition. In SBR2, the vinyl content satisfies the default of the present invention, but the styrene content is lower than the predetermined range of the present invention. As a result, both the ozone crack resistance and the improvement effect of tan δ are still insufficient. Stayed in.

  The rubber composition of Comparative Example A-2 was the same as that of Standard Example A except that the emulsion polymerization styrene-butadiene copolymer rubber (SBR1) was replaced with a comparative solution polymerization styrene-butadiene copolymer rubber (SBR3). It is a comparative rubber composition having the same composition as the rubber composition. In SBR3, both the styrene content and the vinyl content were below the predetermined range of the present invention. As a result, although the ozone crack resistance achieved a good level, no improvement effect was observed for tan δ.

  The rubber composition of Example A-1 is standard example A except that the emulsion-polymerized styrene-butadiene copolymer rubber (SBR1) is replaced with the solution-polymerized styrene-butadiene copolymer rubber (SBR4) according to the present invention. The rubber composition for comparison which has the same composition as the rubber composition. In SBR4, both the styrene content and the vinyl content satisfied the predetermined ranges of the present invention, and as a result, both the ozone crack resistance and tan δ were greatly improved.

  The rubber composition of Comparative Example A-3 was the same as that of Standard Example A except that the emulsion-polymerized styrene-butadiene copolymer rubber (SBR1) was replaced with a comparative solution-polymerized styrene-butadiene copolymer rubber (SBR5). It is a comparative rubber composition having the same composition as the rubber composition. In SBR5, the styrene content is below the predetermined range of the present invention, and conversely, the vinyl content is above the predetermined range of the present invention. As a result, tan δ was almost satisfactory, but the ozone crack resistance was greatly deteriorated.

  The rubber composition of Example A-2 is a standard example A except that the emulsion polymerization styrene-butadiene copolymer rubber (SBR1) is replaced with the solution polymerization styrene-butadiene copolymer rubber (SBR6) according to the present invention. The rubber composition for comparison which has the same composition as the rubber composition. Similarly to SBR4, SBR6 also satisfied both the styrene content and the vinyl content within the predetermined ranges of the present invention, and as a result, succeeded in achieving both ozone crack resistance and tan δ at a high level.

  From the above evaluation results, in order to achieve good ozone crack resistance and grip performance (tan δ) at the same time, it is clear that the rubber component must satisfy the prescription of the present invention. It was.

Standard B, Comparative Examples B-1 to B-3, and Examples B-1 to B-4
For more information about the various compounding components used in the preparation of the formulation components described below various rubber compositions and various test pieces, Standard Example A above, Comparative Examples A-1 to A-3, and Examples A-1 and A -2.

Preparation of various rubber compositions, various test pieces, and various test tires The components other than sulfur and vulcanization accelerator (CBS) shown in Table III below were added in 1.8 L in a compounding amount shown in Table III below. The mixture was kneaded for 3 to 5 minutes in a closed Banbury mixer, and the master batch was discharged when the temperature reached 160 ± 5 ° C. To this master batch, sulfur and a vulcanization accelerator (CBS) having the blending amounts shown in Table III below were added, kneaded with an 8-inch open roll, and Standard Example B and Comparative Examples B-1 to B-3. And the rubber composition of Examples B-1 to B-4 was obtained. Next, various rubber compositions were press vulcanized at 160 ° C. for 20 minutes in a 15 cm × 15 cm × 0.2 cm mold to prepare various target test pieces. Further, for various test tires, emergency pneumatic tires having a tire size of T135 / 70D16 were manufactured under standard molding conditions using various rubber compositions in the cap tread portion.

Measurement of physical properties of various test pieces and various test tires About the various physical properties of the above various test pieces, in the above-mentioned standard example A, comparative examples A-1 to A-3, and examples A-1 and A-2, It was measured according to the same test method as described for “1) ozone crack resistance” and “2) loss tangent (tan δ)”. The tire performance of various test tires was measured according to the following test methods.

3) Ozone crack resistance (tire):
The above various test tires were assembled into rims and allowed to stand for 48 hours at an ozone concentration of 50 pphm and at a temperature of −20 ° C., and then the presence of cracks was visually evaluated.

4) Steering stability:
The various test tires were mounted on a passenger car, and the steering stability was evaluated by grading in five stages based on the feeling during travel. In this evaluation, the higher the grade, the higher the steering stability.

Evaluation of various test pieces and various test tires The results of various physical property measurements 1) to 4) for the above various test pieces and various test tires are also shown in Table III above. As shown in Table III above, in all examples, the composition of the rubber component and all the recipes except the blending amount of the aroma oil are the same, and the total blending of the oil component including the aroma oil is the same. The amount was also adjusted to be the same in all examples (about 50 parts by weight with respect to 100 parts by weight of the rubber component).

  The rubber composition of the standard example B is a comparative rubber composition in which the rubber component is composed only of a comparative solution polymerized styrene-butadiene copolymer rubber (SBR2). As described in Comparative Example A-1 above, SBR-2 has a vinyl content that satisfies the provisions of the present invention, but has a styrene content that is less than the provisions of the present invention. Since the rubber component does not contain polybutadiene rubber (BR), the tan δ of the test piece was at a satisfactory level, but the ozone crack resistance was at an extremely insufficient level. Correspondingly, in terms of tire performance, although the handling stability was at a moderate level, cracks were observed in the test tire assembled with the rim, and the crack resistance was insufficient as a tire. It was confirmed.

  The rubber composition of Comparative Example B-1 was obtained by replacing the comparative solution polymerized styrene-butadiene copolymer rubber (SBR2) with a solution polymerized styrene-butadiene copolymer rubber (SBR4) that satisfies the default of the present invention. A rubber composition for comparison having the same composition as the rubber composition of standard example B. In SBR4 itself, both the styrene content and the vinyl content satisfy the predetermined range of the present invention, but no polybutadiene rubber (BR) is blended in the rubber component, and as a result, tan δ and Although the steering stability as a tire was greatly improved, the effect of improving the ozone crack resistance in the test piece and the test tire was hardly recognized.

  In the rubber composition of Comparative Example B-2, 15 parts by weight of 100 parts by weight of the rubber component (excluding the oil-extended oil component) was replaced with polybutadiene rubber (BR). Reduce the blending amount of polymerized styrene-butadiene copolymer rubber (SBR4), increase the blending amount of aroma oil corresponding to the decrease in oil component oil component of SBR4, and keep the total blending amount of oil components constant A comparative rubber composition having the same composition as the rubber composition of Comparative Example B-1, except that it was maintained at about 50 parts by weight with respect to 100 parts by weight of the rubber component. By blending BR, compared with Comparative Example B-1, tan δ of the test piece and steering stability as a tire were slightly reduced, but the effect of improving ozone crack resistance in the test piece and the test tire was recognized. However, since the blending amount of BR was below the predetermined range of the present invention, it did not reach a satisfactory level.

  In the various rubber compositions of Examples B-1 to B-3, the compounding amount of the polybutadiene rubber (BR) in 100 parts by weight of the rubber component (excluding the oil fraction oil component) is 20 parts by weight and 30 parts by weight, respectively. In accordance with this, the amount of solution polymerized styrene-butadiene copolymer rubber (SBR4) and aroma oil satisfying the default of the present invention is adjusted in the same manner as in Comparative Example B-2. The rubber composition according to the present invention has the same composition as that of Comparative Example B-2. Owing to the increase in the blending amount of BR within the range satisfying the default of the present invention, tan δ of the test piece and a tendency to decrease the steering stability as the tire are observed, but the ozone crack resistance in the test piece and the test tire The properties were also improved to a satisfactory level, and the desired effects of the present invention could be achieved.

  The rubber composition of Example B-4 was the same as that of Example B-3 except that the solution-polymerized styrene-butadiene copolymer rubber (SBR4) was replaced with the solution-polymerized styrene-butadiene copolymer rubber (SBR6). It is the rubber composition which concerns on this invention which has the same composition as this rubber composition. Similarly to SBR4, SBR6 also satisfies the predetermined range of the present invention in terms of styrene content and vinyl content, and as a result, good ozone crack resistance in both the test piece and the test tire. And tan δ or steering stability were compatible.

  In the rubber composition of Comparative Example B-3, the compounding amount of polybutadiene rubber (BR) in 100 parts by weight of the rubber component (excluding the oil-extended oil component) is increased to 50 parts by weight. The same as the rubber composition of Comparative Example B-2, except that the blend amounts of the solution-polymerized styrene-butadiene copolymer rubber (SBR4) and the aroma oil satisfying the default of the invention were adjusted in the same manner as in Comparative Example B-2. A comparative rubber composition having a composition. Although the ozone crack resistance of test specimens and test tires has been greatly improved by increasing the blending amount of BR to an amount that deviates from the predetermined range of the present invention, the tan δ of the test specimens and the operation as a tire are improved. The stability was remarkably lowered, and it was not possible to achieve both ozone crack resistance and steering stability, which are the problems of the present invention.

  From the above evaluation results, it is clear that it is necessary to satisfy the provisions of the present invention for the rubber component to achieve good ozone crack resistance and grip performance (tan δ) at the same time. became.

Claims (3)

(A) 55-83 parts by weight of a solution polymerized styrene-butadiene copolymer rubber (SBR) comprising vinyl derived from 30-45% by weight styrene and 20-50% by weight butadiene;
(B) 45 to 17 parts by weight of polybutadiene rubber (BR);
A rubber composition for a tread part of an emergency pneumatic tire, comprising 100 parts by weight of a rubber component.   The rubber composition for a tread portion of an emergency pneumatic tire according to claim 1, wherein a loss tangent (tan δ) measured at 0 ° C after vulcanization is 0.48 or more. An emergency pneumatic tire characterized in that the rubber composition for a tread portion of the emergency pneumatic tire according to claim 1 or 2 is used in the tread portion.