JP2009242577A - Diene-based rubber composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diene-based rubber composition can improve heat resistance, compression set resistance and durability in a balanced state and suitably usable for a rim cushion part of a tire, etc. <P>SOLUTION: The diene-based rubber composition is obtained by blending 100 pts.wt. of a diene-based rubber blend containing ≥10 wt.% of natural rubber with 3.8-12 pts.wt. of zinc monomethacrylate and 50-90 pts.wt. of a carbon black having a nitrogen adsorption specific surface area N<SB>2</SB>SA (according to JIK K6217-2) of 50-160 m<SP>2</SP>/g, wherein the diene-based rubber composition has a vulcanization accelerator to sulfur weight ratio of 1.2-1.6. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a diene rubber composition. More specifically, the present invention relates to a diene rubber composition suitably used as a rubber material for vulcanization molding of a pneumatic tire rim cushion portion.

  Conventionally, in an automobile vehicle, a pneumatic tire is used in which a rim cushion rubber is disposed on the inner peripheral side of a bead portion that comes into contact with the rim in order to improve the fit between the pneumatic tire and the rim. . By adopting such a structure, the rebound resilience of the rim cushion rubber that is compressed and deformed when the rim is assembled improves the adhesion to the rim, thereby improving the rim fitting property and the rim slip resistance.

  The rim cushion portion is not only subjected to physical stress from the road surface but also directly subjected to stress such as rotational torque. Therefore, since the stress from the road surface and the stress from the rim in the opposite direction are applied to the rim cushion portion, the durability tends to be impaired as compared with other portions of the tire. It is also susceptible to deformation and heat aging due to heat generated by high speed running.

  For this reason, the heat resistance, compression set resistance, and durability of the rim cushion rubber are very important in terms of maintaining the tire internal pressure. If these performances are low, deterioration due to heat, deformation due to various stresses, and fracture The decrease in air pressure caused by the tire increases the deflection of the tire, which leads to a phenomenon such as promoting failure. Here, as a method for improving the compression set resistance, methods such as increasing the amount of carbon black and increasing the amount of vulcanizing compound such as sulfur are used, but in these methods, the breaking strength of the rubber decreases, There are problems such as cracks.

The present applicant has previously described natural rubber and / or polyisoprene rubber 18 to 55 parts by weight, polybutadiene rubber 43 to 80 parts by weight, and styrene-butadiene copolymer rubber as rubber compositions suitably used for rim cushion parts and the like. A rubber composition comprising a blend rubber comprising 2 parts by weight or more and less than 10 parts by weight, wherein the styrene content in the styrene-butadiene copolymer rubber is 35% by weight or less with respect to 100% by weight of the styrene-butadiene copolymer rubber Proposing things. Although the rim cushion part obtained from such a rubber composition is excellent in compression set resistance, further improvement is desired in terms of heat aging resistance and durability.
JP 2007-302715 A

  An object of the present invention is to provide a diene rubber composition that improves heat resistance, compression set resistance, and durability in a well-balanced manner and is suitably used for tire rim cushions and the like.

The object of the present invention is to provide 3.8 to 12 parts by weight of zinc monomethacrylate, 100 parts by weight of diene rubber blend containing 10% by weight or more of natural rubber, nitrogen adsorption specific surface area N ₂ SA (based on JIS K6217-2) Is obtained by blending 50 to 90 parts by weight of carbon black of 50 to 160 m ² / g, and is achieved by a diene rubber composition having a vulcanization accelerator / sulfur weight ratio of 1.2 to 1.6.

  Since the diene rubber composition according to the present invention improves the heat resistance, compression set resistance and durability in a well-balanced manner, it is suitably used as a vulcanization molding material for a rim cushion portion of a pneumatic tire.

  As the diene rubber blend, a natural rubber (NR) containing 10% by weight or more, preferably 10 to 80% by weight is used. If the amount of natural rubber is less than this, the compression set is deteriorated, which is not preferable. Synthetic diene rubbers blended with natural rubber include isoprene rubber (IR), butadiene rubber (BR), chloroprene rubber (CR), butyl rubber (IIR), nitrile rubber (NBR), styrene butadiene rubber (SBR), etc. At least one kind is used, and as the SBR, either emulsion polymerization SBR (E-SBR) or solution polymerization SBR (S-SBR) can be used. As the rubber blend, a blend rubber composed of NR and BR is preferably used.

Zinc monomethacrylate is considered to be coordinated with methacrylic acid with respect to zinc, and is distinguished from zinc dimethacrylate represented by [CH (CH ₃ ) ═CHCOO] ₂ Zn. Actually, Sartomer's product SR709 etc. marketed as zinc monomethacrylate can be used as it is. Further, as an example of synthesis of zinc monomethacrylate, it was obtained by reacting methacrylic acid and zinc oxide with an excess of base, for example, 60 wt% zinc monomethacrylate and 30 wt% zinc dimethacrylate, 10 wt% % Of mixed zinc oxide.
Japanese National Patent Publication No. 11-512776

  Zinc monomethacrylate is used in a proportion of 3.8 to 12 parts by weight, preferably 4.0 to 10 parts by weight, per 100 parts by weight of diene rubber. When the blending ratio of zinc monomethacrylate is less than this, the durability is deteriorated. On the other hand, when it is used at a ratio higher than this, the heat resistance is deteriorated, which is not preferable. Here, zinc monomethacrylate can be used alone as a zinc compound without using zinc oxide, and can be used in combination with zinc oxide or the like if the total amount of the zinc compound is within 12 parts by weight.

Further, as carbon black, nitrogen adsorption specific surface area N ₂ SA (conforming to JIS K6217-2) 50 to 160 m ² / g, preferably 60 to 140 m ² / g is 50 to 90 per 100 parts by weight of diene rubber. Part by weight, preferably 60-80 parts by weight. As the carbon black having such nitrogen adsorption specific surface area N ₂ SA, carbon black of SAF, ISAF, HAF grade is used, and carbon black having a smaller nitrogen adsorption specific surface area N ₂ SA, for example, FEF, GPF carbon black When is used, high rigidity cannot be satisfied. Also, if carbon black is used in a smaller proportion, the reinforcing effect of carbon black will not be exhibited and wear resistance will be reduced, while if it is used more than this, the breaking strength of rubber will be reduced. , Durability becomes worse.

  In the diene rubber composition, 0.5 to 3 parts by weight of sulfur as a vulcanizing agent as a rubber compounding agent, preferably 1 to 2 parts by weight, a thiazole type (MBT, MBTS, ZnMBT, etc.), a sulfenamide type ( CBS, DCBS, BBS, etc.), guanidine (DPG, DOTG, OTBG, etc.), thiuram (TMTD, TMTM, TBzTD, TETD, TBTD, etc.), dithiocarbamate (ZTC, NaBDC, etc.), xanthate ( 0.6-4 parts by weight, preferably 1-2.5 parts by weight of a vulcanization accelerator such as ZnBX etc., is used, so that the vulcanization accelerator / sulfur weight ratio is 1.2-1.6, preferably 1.3-1.5. Added in proportions. When the vulcanization accelerator / sulfur weight ratio is smaller than this, the heat resistance becomes inferior, while when it is larger, the durability becomes inferior.

  In the diene rubber composition containing the above components as essential components, a compounding agent generally used as a compounding agent for rubber, for example, reinforcing agents or fillers such as talc, clay, graphite, calcium silicate, etc. Further, processing aids such as stearic acid, paraffin wax and aroma oil, anti-aging agents, plasticizers and the like are appropriately blended and used as necessary.

  The composition was prepared by kneading by a general method using a kneader such as a kneader or a Banbury mixer and an open roll, and the obtained composition was vulcanized according to the diene rubber used. It is vulcanized at temperature to form a rim cushion part (indicated by reference numeral 3 in FIG. 1).

  Next, the present invention will be described with reference to examples.

Example 1
Natural rubber (STR20) 50 parts by weight Butadiene copolymer rubber (Nippon Zeon product NIPOL BR1220) 50 〃
HAF carbon black (Tokai carbon product seast 300 70 〃
: Nitrogen adsorption specific surface area N ₂ SA 81m ² / g)
Zinc monomethacrylate (Sartomer product SR709) 8 〃
Anti-aging agent (Sumitomo Chemical Antigen 6C) 3 〃
Sulfur (Tsurumi Chemical Co., Ltd. product fine powder sulfur with Jinhua seal oil, sulfur content 95%) 1.5 〃
Vulcanization accelerator (Ouchi Emerging Chemical Industry Noxeller NS-P) 2

Among the above components, the components other than the vulcanization accelerator and sulfur were kneaded with a 3 L closed mixer for 5 minutes and released when the temperature reached 150 ° C. to obtain a master batch. A vulcanization accelerator and sulfur were added to the masterbatch and kneaded with an open roll to obtain a diene rubber composition (vulcanization accelerator / sulfur weight ratio = 1.40).

Example 2
In Example 1, the amount of zinc monomethacrylate was changed to 4 parts by weight, and 2 parts by weight of zinc white (3 types of Zinc Chemical Products Zinc Oxide) was used.

Comparative example 1 (standard example)
In Example 1, 4 parts by weight of zinc white (3 types of zinc oxide) was used instead of zinc monomethacrylate, and the sulfur content was changed to 2 parts by weight (vulcanization accelerator / sulfur weight ratio). = 1.05).

Comparative Example 2
In Example 1, 4 parts by weight of zinc white (3 types of zinc oxide) was used instead of zinc monomethacrylate.

Comparative Example 3
In Example 1, the same amount of GPF carbon black (Tokai carbon product HTC # G: nitrogen adsorption specific surface area 26 m ² / g) was used instead of HAF carbon black, and the amount of zinc monomethacrylate was changed to 7 parts by weight. Used.

Comparative Example 4
In Example 1, the amount of zinc monomethacrylate was changed to 3 parts by weight.

Comparative Example 5
In Example 1, the amount of zinc monomethacrylate was changed to 14 parts by weight.

Comparative Example 6
In Example 1, the amount of zinc monomethacrylate was changed to 7 parts by weight, and the amount of sulfur was changed to 2 parts by weight (vulcanization accelerator / sulfur weight ratio = 1.05).

Comparative Example 7
In Example 1, the amount of zinc monomethacrylate was changed to 7 parts by weight and the amount of sulfur was changed to 1 part by weight (vulcanization accelerator / sulfur weight ratio = 2.10).

Comparative Example 8
In Example 1, natural rubber was not used, but the amount of butadiene copolymer rubber was changed to 100 parts by weight, and the amount of zinc monomethacrylate was changed to 7 parts by weight.

The diene rubber composition obtained in each of the above Examples and Comparative Examples was vulcanized at 150 ° C. for 30 minutes to obtain a predetermined vulcanized rubber test piece. About the obtained vulcanized rubber test piece, heat aging resistance was obtained. The compression set and the bending fatigue resistance were measured.
Heat aging resistance: Measured according to JIS K6251, 80% elongation at break / initial break elongation after 96 hours
And an index with the value obtained in the standard example as 100
(The larger the value, the better the heat aging resistance)
Compression set: Compliant with JIS K6262, measuring the distortion rate after 22 hours at 70 ° C with a distortion rate of 25%.
The reciprocal with the value obtained in 100 as 100 is shown as an exponent.
(The larger the value, the better the compression set)
Bending fatigue resistance: Measured according to JIS K6260-1999, crack length after bending 30,000 times, standard
Indicated by an index where the value obtained in the example is 100
(The larger this value, the better the bending fatigue resistance)

The results obtained are shown in the following table.
table
Example Compression set Heat resistance Aging resistance Bending fatigue resistance
Example 1 105 110 105
〃 2 105 108 100
Comparative Example 1 100 100 100
〃 2 105 105 95
３ 3 100 95 120
４ 4 110 105 95
５ 5 95 120 110
６ 6 95 105 100
〃 7 110 115 95
８ 8 105 95 105

From the above results, the following can be said.
(1) In each example, heat aging resistance, compression set resistance and durability are improved in a well-balanced manner.
(2) Compared with the comparative example 1 which is a standard example, bending fatigue resistance deteriorates only by reducing the amount of sulfur without blending zinc monomethacrylate (Comparative Example 2).
(3) When GPF is used as a carbon black grade, the compression set characteristics are deteriorated as compared with Comparative Example 1 which is a standard example (Comparative Example 3).
(4) Bending fatigue resistance (durability) deteriorates when the amount of zinc monomethacrylate is blended at a ratio equal to or less than the specified amount as compared with Comparative Example 1 which is a standard example (Comparative Example 4).
(5) Compared with the comparative example 1 which is a standard example, when the amount of zinc monomethacrylate is blended at a ratio of a specified amount or more, the heat aging resistance deteriorates (Comparative Example 5).
(6) Compared with Comparative Example 1 which is a standard example, even if the amount of zinc monomethacrylate is within the specified amount, if the vulcanization accelerator / sulfur weight ratio is smaller than the specified range, the heat aging resistance Worsens (Comparative Example 6).
(7) Bending fatigue resistance when the vulcanization accelerator / sulfur weight ratio is larger than the specified range even if the amount of zinc monomethacrylate is within the specified amount as compared with Comparative Example 1 which is a standard example. Property (durability) deteriorates (Comparative Example 7).
(8) Compared with Comparative Example 1 which is a standard example, even if the amount of zinc monomethacrylate is within the specified amount, compression set characteristics deteriorate if natural rubber is not used (Comparative Example 8).

It is principal part sectional drawing of a pneumatic tire.

Explanation of symbols

1 Bead Filler 2 Bead Core 3 Rim Cushion 4 Chafer 5 Carcass

Claims (3)

Zinc monomethacrylate 3.8-12 parts by weight, nitrogen adsorption specific surface area N ₂ SA (conforms to JIS K6217-2) 50-160 m ² / g per 100 parts by weight of diene rubber blend containing 10% by weight or more of natural rubber A diene rubber composition comprising 50 to 90 parts by weight of carbon black and having a vulcanization accelerator / sulfur weight ratio of 1.2 to 1.6.   The diene rubber composition according to claim 1, which is used as a rubber material for vulcanization molding of a pneumatic tire rim cushion portion.   A pneumatic tire having a rim cushion portion vulcanized and molded from the diene rubber composition according to claim 2.

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