TECHNICAL FIELD

The present invention relates to a pneumatic tire and a crosslinked rubber composition.

BACKGROUND OF THE INVENTION

It is known that generally a crosslinked rubber composition used for a tire tread is excellent in breaking resistance and abrasion resistance as its glass transition temperature (Tg) becomes lower (for example, Patent Document 1, etc.). One of factors thereof is thought to be such that as the Tg becomes lower, an elastic modulus, in a range of frequency of stimulus received from unevenness of road surface, of a crosslinked rubber composition decreases, which allows the crosslinked rubber composition to follow the unevenness easily.

However, a lower Tg does not necessarily lead to excellent breaking resistance and abrasion resistance, and there is an exception. Namely, sometimes there is a phenomenon such that though a hardness of a crosslinked rubber composition is high, good results cannot be obtained from measurement of abrasion resistance of this crosslinked rubber composition and a rubber product thereof.

In order to make a mechanism of causing such an exception clear, breakage and friction phenomena have been observed by means of various methods. However, the mechanism has not been made clear completely.

Meanwhile, an X-ray computerized tomography is known as a technology for analyzing a material constituting a solid sample and a low density region contained in an inside thereof. For example, Patent Document 2 describes a method of visually analyzing a material constituting a friction member and a low density region contained inside thereof. However, analyzing a sample material in a state, such as elongation, of being applied with an external energy or analyzing a density of the material is not described in Patent Document 2.

PATENT DOCUMENTS

Patent Document 1: JP 2013-007025 APatent Document 2: JP 2009-085732 A

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

An object of the present invention is to provide a pneumatic tire being excellent in abrasion resistance and a crosslinked rubber composition.

Means to Solve the Problem

The inventors of the present invention have made intensive studies, and as a result, have found that growth of cracking generated inside a crosslinked rubber composition can be inhibited and abrasion resistance can be enhanced more by increasing a low density region at elongation by an applied stress of 1.5 MPa, decreasing a void portion at elongation by an applied stress of 3.0 MPa and decreasing a glass transition temperature, and thus have completed the present invention.

Namely, the present invention relates to a pneumatic tire comprising bead cores provided on a pair of right and left bead portions, respectively, a carcass ply extending from a crown portion to the both bead portions through both side wall portions and moored to the bead cores, an inner liner disposed at an inner side than the carcass ply in a direction of a tire diameter, and a tread disposed at an outer side than the carcass ply in a direction of a tire diameter and having a volume of the low density region of 35% or more at elongation by an applied stress of 1.5 MPa, a volume of the void portion of 7.5% or less at elongation by an applied stress of 3.0 MPa and a glass transition temperature of −20° C. or lower.

Further, the present invention relates to a crosslinked rubber composition having a volume of the low density region of 35% or more at elongation by an applied stress of 1.5 MPa, a volume of the void portion of 7.5% or less at elongation by an applied stress of 3.0 MPa and a glass transition temperature of −20° C. or lower.

It is preferable that the rubber component is a rubber component comprising one or more of rubber components comprising a conjugated diene compound.

It is preferable that the above-mentioned low density region is a region having a density of 0.1 to 0.8 time the density of a crosslinked rubber composition before the elongation.

It is preferable that the above-mentioned void portion is a region having a density of 0 to 0.1 time the density of a crosslinked rubber composition before the elongation.

It is preferable that a method of evaluating volumes of the low density region and the void portion is an X-ray computerized tomography.

It is preferable that a decay time of a phosphor for converting the X-ray into a visible light is 100 ms or less.

It is preferable that a luminance of the X-ray is 1010photons/s/mrad2/mm2/0.1% bw or more.

Effect of the Invention

According to the pneumatic tire of the present invention comprising a tread having a large volume of the low density region at elongation by an applied stress of 1.5 MPa, a small volume of the void portion at elongation by an applied stress of 3.0 MPa and a low glass transition temperature, and to the crosslinked rubber composition of the present invention having a large volume of the low density region at elongation by an applied stress of 1.5 MPa, a small volume of the void portion at elongation by an applied stress of 3.0 MPa and a low glass transition temperature, it is possible to provide a pneumatic tire and a crosslinked rubber composition being excellent in abrasion resistance.

