JP5630540B1 - Rubber composition for tire sidewall and pneumatic tire using the same - Google Patents

Abstract

Conventionally, in a rubber composition for a tire sidewall, a hydrocarbon wax is blended in order to prevent generation of rubber cracks due to ozone. However, when the wax is blended, there is a problem that the rubber surface gradually elutes and solidifies during long-term use, and the rubber surface becomes white and the appearance deteriorates. An object of the present invention is to provide a rubber composition for a tire sidewall and a pneumatic tire using the same, which solve the problem. The wax and the polybutene resin are mixed with 1 to 2.5 parts by weight of a wax and 1.0 to 5.0 parts by weight of a polybutene resin per 100 parts by weight of a diene rubber containing natural rubber. A rubber composition for a tire sidewall characterized by having a molar ratio of 0.8 to 3.2 as the former / the latter, and a pneumatic tire using the rubber composition as a sidewall. [Selection figure] None

Description

  TECHNICAL FIELD The present invention relates to a rubber composition for tire sidewalls and a pneumatic tire using the same, and more specifically, prevents appearance defects due to whitening without deteriorating various characteristics required for tire sidewalls. The present invention relates to a possible rubber composition for a tire sidewall and a pneumatic tire using the same.

  Conventionally, in a rubber composition for a tire sidewall, a hydrocarbon wax is usually blended in order to prevent cracking of rubber due to ozone. However, when such a wax is blended, there is a problem that the rubber surface gradually elutes (bleeds) and solidifies during long-term use, and as a result, the rubber surface becomes white and the appearance deteriorates.

For this reason, for example, the following Patent Document 1 discloses a rubber composition for a tire sidewall that contains 15 to 100 parts by weight of a photocatalyst and 100% by weight of a diene rubber and does not contain wax. In Patent Document 2, a rubber component selected from the group consisting of natural rubber, polyisoprene rubber, polybutadiene rubber, and styrene-butadiene copolymer rubber and a wax are used as a core agent, and the surface of the core agent has a melting point of 120 to 120. A rubber composition for a tire sidewall is disclosed, which includes a microcapsule coated with a 180 ° C. thermoplastic resin as a wax.
However, in the industry where the recent improvement in tire quality is severely demanded, there is a demand for a technology that can further solve the problem of poor appearance of tire sidewalls.

JP 2007-284522 A JP 2006-328144 A

  An object of the present invention is to provide a rubber composition for a tire sidewall capable of preventing the occurrence of poor appearance due to whitening without deteriorating various characteristics required for the tire sidewall, and a pneumatic tire using the same. It is in.

As a result of intensive studies, the inventors have formulated a specific amount of wax and a specific amount of polybutene resin in a rubber component having a specific composition, and set the molar ratio of wax and polybutene resin to a specific range. The present inventors have found that the above problems can be solved and have completed the present invention.
That is, the present invention is as follows.

1. 1 to 2.5 parts by mass of wax and 1.0 to 5.0 parts by mass of polybutene resin are blended with respect to 100 parts by mass of diene rubber containing natural rubber, and the molar ratio of the wax and polybutene resin is A rubber composition for a tire sidewall, wherein the former / the latter is within a range of 0.8 to 3.2.
2. 2. The rubber composition for a tire sidewall according to 1 above, wherein the polybutene resin has a weight average molecular weight of 500 to 5,000.
3. 3. The rubber composition for a tire side wall according to the above 1 or 2, wherein the hydrocarbon most contained in the wax has 40 or less carbon atoms.
4). 4. The rubber composition for a tire sidewall according to any one of 1 to 3, wherein a blending amount of the natural rubber is 30 to 50% by mass with respect to the entire diene rubber.
5. Oil is further blended in the rubber composition for a tire sidewall, and the blending amount of the oil, the wax and the polybutene resin is 17 parts by mass or less with respect to 100 parts by mass of the diene rubber. 5. The rubber composition for a tire sidewall according to any one of 1 to 4 above.
6). A pneumatic tire using the tire sidewall rubber composition according to any one of 1 to 5 as a sidewall.

  According to the present invention, a specific amount of wax and a specific amount of polybutene resin are blended with a rubber component having a specific composition, and the molar ratio of the wax and polybutene resin is set to a specific range, so that various requirements for tire sidewalls are obtained. It is possible to provide a rubber composition for a tire sidewall that can prevent appearance defects due to whitening without deteriorating characteristics, and a pneumatic tire using the rubber composition.

  Hereinafter, the present invention will be described in more detail.

(Diene rubber)
The diene rubber used in the present invention contains natural rubber (NR) as an essential component. The blending amount of NR is preferably 30 to 50% by mass with respect to the whole diene rubber from the viewpoint that the effect of the present invention is improved. In addition to NR, other diene rubbers can be used. For example, isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber ( NBR) and the like. These may be used alone or in combination of two or more. The molecular weight and microstructure are not particularly limited, and may be terminally modified with an amine, amide, silyl, alkoxysilyl, carboxyl, hydroxyl group or the like, or may be epoxidized.

(wax)
The wax used in the present invention is not particularly limited, and any wax conventionally used for the purpose of preventing the occurrence of rubber cracks can be used, for example, paraffin wax, paraffin synthetic wax, Examples thereof include hydrocarbon waxes such as polyethylene wax. These waxes usually contain hydrocarbons having 20 to 50 carbon atoms. Among these, from the viewpoint of improving the effect of the present invention, it is preferable that the hydrocarbon most contained in the wax has 40 or less carbon atoms.
Here, “the carbon number of the hydrocarbon most contained in the wax” can be obtained from the peak top of the carbon number distribution of the chromatogram obtained by gas chromatography, for example.
For example, gas chromatography conditions include:
Gas chromatograph: GC-8A (manufactured by Shimadzu Corporation)
Column: OV-1
Carrier gas: N ₂
Oven temperature: 250 ° C
Detector: FID
Detector temperature: 250 ° C
Is mentioned.

(Polybutene resin)
The polybutene resin used in the present invention is a known compound and is commercially available. From the viewpoint of improving the effect of the present invention, the weight average molecular weight (Mw) of the polybutene resin is preferably 500 to 5,000, and more preferably 500 to 2,000.
In addition, Mw shall be measured by standard polystyrene conversion by gel permeation chromatography (GPC).
Such polybutene resins are commercially available, for example, as HV series from JX Nippon Oil & Energy.

  According to the study by the present inventors, it is speculated that the polybutene resin acts to prevent the sidewall surface from becoming white by suppressing the crystallization of the wax bleed on the sidewall surface and closely adhering to the surface. The

(filler)
In addition to the above, the rubber composition for a tire sidewall of the present invention can contain various fillers. The filler is not particularly limited and may be appropriately selected depending on the application. Examples thereof include carbon black, silica, and inorganic filler. Examples of the inorganic filler include clay, talc, and calcium carbonate.

(Combination ratio of rubber composition for tire sidewall)
The rubber composition for a tire sidewall of the present invention contains 1 to 2.5 parts by weight of a wax and 1.0 to 5.0 parts by weight of a polybutene resin, and the molar ratio of the wax and the polybutene resin is: The former / the latter is characterized by being in the range of 0.8 to 3.2.
When the blending amount of the wax is less than 1 part by mass, it is impossible to prevent rubber cracking due to ozone. Conversely, when it exceeds 2.5 parts by mass, the appearance is remarkably deteriorated. The more preferable amount of the wax is 1.0 to 2.0 parts by mass.
When the blending amount of the polybutene resin is less than 0.5 parts by mass, the blending amount is too small to achieve the effects of the present invention. Conversely, when the amount exceeds 5.0 parts by mass, poor appearance occurs. A more preferable blending amount of the polybutene resin is 1.0 to 2.5 parts by mass.
When the molar ratio of the wax and the polybutene resin is less than 0.8 or exceeds 3.2, the appearance is deteriorated.

  The number of moles of wax referred to in the present invention is the number of moles of hydrocarbons contained most in the wax.

The tire sidewall rubber composition according to the present invention includes a tire sidewall rubber such as a vulcanization or crosslinking agent, a vulcanization or crosslinking accelerator, a filler, an anti-aging agent, and a plasticizer in addition to the components described above. Various additives generally blended in the composition can be blended, and such additives can be kneaded by a general method to form a composition, which can be used for vulcanization or crosslinking. The blending amounts of these additives can be set to conventional general blending amounts as long as the object of the present invention is not violated.
Further, as described above, the rubber composition for a tire sidewall of the present invention is preferably introduced into the sidewall of the pneumatic tire according to a conventional method for producing a pneumatic tire.

  EXAMPLES Hereinafter, although an Example and a comparative example further demonstrate this invention, this invention is not restrict | limited to the following example.

Examples 1-9 and Comparative Examples 1-9
Sample Preparation In the formulation (parts by mass) shown in Table 1, the components other than the vulcanization accelerator and sulfur were kneaded for 5 minutes in a 1.7 liter closed Banbury mixer, and then released outside the mixer at about 150 ° C. Cooled to room temperature. Subsequently, a vulcanization accelerator and sulfur were added to the composition and kneaded with an open roll to obtain a rubber composition for a tire sidewall. Next, the rubber composition for tire sidewall obtained was press vulcanized in a predetermined mold at 170 ° C. for 10 minutes to obtain a vulcanized rubber test piece, and the physical properties of the vulcanized rubber test piece by the following test method Was measured.

Appearance: By standing for 2 weeks in an oven at 40 ° C., it was visually evaluated according to the following criteria.
Point 1: Overall color changed to white Point 2: About 30% of the area changes to white Point 3: Overall is dull Point 4: About 30% of the area is dull.
Score 5: Invariant This was carried out with n = 3, and the average score was taken as the evaluation score.

  Tensile test: Based on JIS K 6251 (JIS No. 3 dumbbell), a tensile test was performed at room temperature, and tensile strength (TB) and elongation at break (EB) were measured. Comparative example 1 was set to 100 and indicated as an index. The larger the index, the higher the strength.

Ozone resistance: Ozone resistance was tested under test conditions in accordance with JIS K6259 at 40% elongation, 50 pphm, 40 ° C., 48 hours, and visually evaluated according to the following criteria.
Number of points 1: Cracks or cuts of 3 mm or more Number of points 2: Deep and large cracks (less than 1 to 3 mm)
Score 3: Deep crack and relatively large (less than 1mm)
Score 4: Invisible to the naked eye but can be confirmed with a 10x magnifier. Score 5: No crack confirmed with the naked eye and a 10x magnifier. This was performed at n = 3 and the average score was taken as the evaluation score.

  The results are also shown in Table 1.

* 1: NR (TSR20)
* 2: BR (Nipol BR1220 manufactured by Nippon Zeon Co., Ltd.)
* 3: Carbon black (Niteron Carbon Co., Ltd. Niteron # 10S)
* 4: Zinc oxide (3 types of zinc oxide manufactured by Shodo Chemical Industry Co., Ltd.)
* 5: Stearic acid (beef stearic acid YR manufactured by NOF Corporation)
* 6: Anti-aging agent-1 (SANTOFLEX 6PPD manufactured by FLEXSYS)
* 7: Anti-aging agent-2 (Antigen RD-G, manufactured by Sumitomo Chemical Co., Ltd.)
* 8: Wax-1 (Onouchi Shin Chemical Co., Ltd. Sannok. Carbon number of the most abundant hydrocarbons determined by gas chromatography = 32)
* 9: Wax-2 (Nippon Seiki Co., Ltd. Hi-mac-1080. Carbon number of the most abundant hydrocarbon determined by gas chromatography = 45)
* 10: Oil (Diana Process Oil AH-20 manufactured by Idemitsu Kosan Co., Ltd.)
* 11: Vulcanization accelerator (Ouchi Shinsei Chemical Co., Ltd. Noxeller CZ-G)
* 12: Sulfur (fine powdered sulfur with Jinhua seal oil from Tsurumi Chemical Co., Ltd.)
* 13: Polybutene resin-1 (JX Nippon Oil & Energy Corporation HV-100, weight average molecular weight = 980)
* 14: Polybutene resin-2 (JX Nippon Oil & Energy Corporation HV-300, weight average molecular weight = 1,400)

As is clear from Table 1 above, the rubber composition for tire sidewall prepared in the examples is prepared by blending a specific amount of wax and a specific amount of polybutene resin with a rubber component having a specific composition, and wax and polybutene. Since the molar ratio of the resin was set within a specific range, it was found that the appearance failure due to whitening was prevented and ozone resistance was good as compared with Comparative Example 1. It has also become clear that various properties required for tire sidewalls are not adversely affected. In Example 7, since the blending amount of oil, wax and polybutene resin exceeds 17 parts by mass with respect to 100 parts by mass of the diene rubber, the appearance is slightly deteriorated. In Examples 8 to 9, since the carbon number of the hydrocarbon most contained in the wax exceeds 40, the ozone resistance is slightly deteriorated.
On the other hand, in Comparative Example 2, although the blending amount of the wax was reduced as compared with Comparative Example 1, neither appearance nor ozone resistance was improved.
In Comparative Example 3, since the blending amount of the polybutene resin exceeded the upper limit specified in the present invention and the molar ratio of the wax and the polybutene resin was less than the lower limit specified in the present invention, the appearance deteriorated.
Since the compounding quantity of the polybutene resin exceeded the upper limit prescribed | regulated by this invention in the comparative example 4, the external appearance deteriorated.
In Comparative Examples 5 and 6, since the molar ratio of the wax and the polybutene resin was less than the lower limit specified in the present invention, the appearance deteriorated.
Since the molar ratio of the wax and polybutene resin exceeded the upper limit prescribed | regulated by this invention in the comparative example 7, the external appearance deteriorated.
Since the comparative example 8 did not mix | blend polybutene resin, both the external appearance and ozone resistance deteriorated.
In Comparative Example 9, since no wax was blended, both appearance and ozone resistance deteriorated.

Claims (6)

  1 to 2.5 parts by mass of wax and 1.0 to 5.0 parts by mass of polybutene resin are blended with respect to 100 parts by mass of diene rubber containing natural rubber, and the molar ratio of the wax and polybutene resin is A rubber composition for a tire sidewall, wherein the former / the latter is within a range of 0.8 to 3.2.   The rubber composition for a tire sidewall according to claim 1, wherein the polybutene resin has a weight average molecular weight of 500 to 5,000.   The rubber composition for a tire sidewall according to claim 1 or 2, wherein the hydrocarbon most contained in the wax has 40 or less carbon atoms.   The rubber composition for a tire sidewall according to any one of claims 1 to 3, wherein a blending amount of the natural rubber is 30 to 50% by mass with respect to the entire diene rubber.   Oil is further blended in the rubber composition for a tire sidewall, and the blending amount of the oil, the wax and the polybutene resin is 17 parts by mass or less with respect to 100 parts by mass of the diene rubber. The rubber composition for tire sidewalls in any one of Claims 1-4.   A pneumatic tire using the rubber composition for a tire sidewall according to any one of claims 1 to 5 as a sidewall.