JP2015101636A - Rubber composition for tire, and destruction test method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rubber composition for a tire which has excellent tread break-off resistance performance.SOLUTION: A rubber composition for a tire is to be broken under a dynamic torsional amplitude of 250% or more when dynamic torsional deformation in synchronization with compressive strain is applied during dynamic compressive deformation at 70-150°C. A destruction test method for a rubber crosslinked material includes applying simultaneously combined deformation of dynamic compressive deformation and dynamic torsional deformation to a sample at 70-150°C.

Description

The present invention relates to a rubber composition for tires and a destructive test method for a crosslinked rubber product obtained by crosslinking the composition.

In recent years, tires with excellent fuel efficiency have been desired due to increasing interest in environmental problems. As one of the methods for improving the low fuel consumption, a method of replacing carbon black as a filler with silica is known. However, this method has a problem that mechanical strength (breaking strength) is lowered, cut resistance and chipping resistance are deteriorated, and wear resistance is lowered. For the purpose of improving fuel economy, an attempt has been made to improve the dispersibility of silica by adding a specific polar group to the rubber so as to have an affinity for silica in a rubber composition containing silica. However, there is still room for improvement in terms of improving the mechanical strength, wear resistance, and fuel efficiency in a balanced manner.

The mechanical strength has been conventionally evaluated by breaking strength and breaking elongation by a uniaxial tensile test. However, the deformation that the tread undergoes during running is rarely uniaxial tension, and is often subject to shear and torsion deformation under load compression due to vehicle weight, and in the uniaxial tension test, the mechanical strength of the tread is superior or inferior. In many cases, it is difficult to determine the above. In addition, the difference in mechanical strength can be made remarkable by bringing the rubber specimen to a high temperature state. However, even if the uniaxial tensile test is performed under high temperature conditions, the mechanical strength of the tread is superior or inferior. Is often not consistent with the order of tires.

The tire tread is subjected to torsion and shear strain while being compressed by the vehicle weight. In order to apply such strain to a rubber test piece, the rubber composition is often bonded to two support plates to be deformed. However, in a laminated body to which vulcanized rubber is bonded, when it is repeatedly deformed, the adhesive layer is often broken or peeled between the rubber and the support. Patent Document 1 discloses a method of vulcanizing and bonding a vulcanized rubber and a metal plate with an adhesive, but still often peels between the rubber and the metal plate at the time of large deformation or high-speed deformation, It was difficult to correctly evaluate the durability of the different types of rubber laminates. Therefore, there are some cases where tread chipping occurs even when the rubber composition thus improved is applied to a tire of an actual vehicle, and the tread chipping when applied to an actual vehicle is suppressed and the rubber composition has high durability. It is desired to provide.

JP 2001-11366 A

An object of the present invention is to solve the above-mentioned problems and to provide a tire rubber composition having excellent tread chipping resistance.

That is, the present invention relates to a rubber composition for a tire that is destroyed at a dynamic torsional amplitude of 250% or more when a dynamic torsional deformation synchronized with the compressive strain is applied at 70 to 150 ° C. Related to things.

It is preferable that the compression load of dynamic compression deformation is 50 kPa to 10 MPa.

It is preferable that the period of dynamic compression deformation is 1 to 100 Hz.

It is preferable to contain 10 to 150 parts by mass of carbon black or white filler with respect to 100 parts by weight of the diene rubber component.

Furthermore, it is preferable to contain 0.5-5 mass parts of crosslinking agents with respect to 100 weight parts of diene rubber components.

Moreover, this invention relates to the pneumatic tire produced using the said rubber composition for tires.

Furthermore, this invention relates to the fracture test method of the crosslinked rubber body including the process of simultaneously applying the composite deformation of the dynamic compression deformation and the dynamic torsion deformation to the sample at 70 to 150 ° C.

According to the present invention, at 70 to 150 ° C., when a dynamic torsional deformation synchronized with the compressive strain is applied during the dynamic compressive deformation, the rubber composition for a tire is destroyed when the dynamic torsional amplitude is 250% or more. Therefore, the tread produced using the rubber composition is excellent in chipping resistance.
Moreover, according to the method for destructive testing of a crosslinked rubber product of the present invention, since it includes a step of simultaneously applying a composite deformation of dynamic compression deformation and dynamic torsion deformation to a sample at 70 to 150 ° C. It is possible to evaluate the chipping resistance of the tire in a state very close to.

It is an example of the schematic diagram which shows the twist deformation | transformation in a columnar test piece. It is an example of the schematic diagram which shows the sample for a measurement, and the dynamic compressive deformation and dynamic torsion deformation which are added to it. It is a schematic diagram which shows the preferable rubber-metal composite used for a compression torsion test. It is a schematic diagram which shows a cylindrical rubber-metal composite. It is a schematic diagram of the apparatus which forms a guideline.

In the present invention, when dynamic torsional deformation synchronized with compressive strain is applied during dynamic compression deformation at 70 to 150 ° C., the dynamic torsional amplitude is 250% or more, preferably 270% or more. It is a rubber composition for tires. That is, at 70 to 150 ° C., the dynamic torsional amplitude is 250% or more when applied to the rubber composition while synchronizing dynamic compression and shear deformation, which are deformation modes actually input from the road surface during tire travel. Since it is a rubber composition having the property of being destroyed at a time, it is excellent in chipping resistance performance in an actual vehicle.

Specifically, the crosslinked product of the rubber composition periodically applies pressure (compression load) and repeatedly applies dynamic compressive deformation, thereby causing the compressive deformation repeatedly input to the tire due to the vehicle weight when the vehicle travels. Synchronously with this, torsional deformation is periodically applied, and dynamic torsional deformation is repeatedly applied to give a torsional deformation that is input to the tire when turning, resulting in a dynamic torsion exceeding a predetermined value. It has amplitude, that is, mechanical strength. Therefore, compared to the conventional evaluation method based only on the uniaxial tensile test, since it is a rubber composition having a predetermined mechanical strength when a destructive test is performed in an environment closer to the use conditions, chipping resistance in an actual vehicle is reduced. The performance is also excellent.

Specifically, a rubber composition in which dynamic compression deformation and dynamic torsion deformation are input while increasing dynamic torsion amplitude and the torsion amplitude (torsional displacement) at the time of fracture of the rubber composition is 250% or more. It is a thing.

In particular, when dynamic compression deformation reaches the maximum displacement point (maximum strain of dynamic compression deformation), input is to be synchronized so that dynamic torsion deformation becomes the maximum displacement point (maximum strain of dynamic torsion deformation). Therefore, the correlation with the chipping performance of the actual vehicle is further enhanced, and in this case, the rubber composition having a dynamic torsional amplitude greater than or equal to a predetermined value is very excellent.

The rubber composition of the present invention is one that breaks when the dynamic torsional amplitude is 250% or more when dynamic torsional deformation synchronized with the compressive strain is applied during dynamic compressive deformation. The deformation corresponds to repeated deformation due to vehicle weight, and the dynamic torsion deformation corresponds to deformation received from the road surface during turning.

Here, in the rubber composition, the dynamic compression deformation and the dynamic torsional deformation are synchronized. Specifically, in order to reproduce the actual vehicle conditions, the maximum displacement point of the dynamic compression deformation is the torsional deformation. It is desirable to match the maximum displacement point, and the minimum displacement point (no load point) of dynamic compressive deformation matches the zero displacement point of dynamic torsional deformation.

If both dynamic compression deformation and dynamic torsional deformation are repetitive deformations that satisfy the above conditions, the waveform is not defined, but is preferably a sine wave that matches the dynamic input of the actual vehicle.

The cycle of dynamic compression deformation corresponds to the rolling cycle during actual vehicle travel, and is preferably 100 Hz or less at a practical level including a race, and more preferably 20 Hz or less corresponding to 120 km / h or less which is a normal use condition. . The lower limit of the period is not particularly limited, but considering slow driving at the intersection, it is preferably 1 Hz or more corresponding to a speed of 10 km / h, more preferably 2 Hz or more corresponding to a speed of 20 km / h.

Since dynamic compression deformation corresponds to deformation due to vehicle weight, the amplitude is defined by pressure, and the pressure applied at the maximum amplitude (compression load) is preferably 10 MPa or less, more preferably 3 MPa or less, More preferably, it is 1.5 MPa or less. The lower limit of the pressure is preferably 50 kPa or more, more preferably 150 kPa or more, and still more preferably 300 kPa or more from the viewpoint of a pressure corresponding to half the vehicle weight. By setting the pressure within the above range, the chipping resistance when used in a tire can be evaluated well.

The period of the dynamic torsional deformation is preferably determined by the period of the dynamic compression deformation from the viewpoint of synchronizing the dynamic compression deformation and the torsional deformation. Specifically, when the origin of displacement 0 is placed at the center position of dynamic torsional deformation, half the period of dynamic compression deformation is used. When the origin of displacement 0 is placed at the minimum displacement position of dynamic torsional deformation, dynamic is applied. It is preferable to have the same cycle as the compression deformation.

When synthesizing and applying combined deformation of dynamic compression deformation and dynamic torsional deformation, the rubber composition is destroyed at 70 to 150 ° C. while increasing the dynamic torsional amplitude (dynamic torsional deformation amplitude). Use the method. Specifically, measurement is performed while gradually increasing the amplitude of dynamic torsional deformation until the rubber composition breaks, and the superiority or inferiority of chipping resistance can be determined by the torsional displacement (dynamic torsional amplitude) at the time of destruction. If the dynamic torsional amplitude is 250% or more, it can be evaluated that the performance is excellent.

Here, the dynamic torsional amplitude is the dynamic torsional displacement with respect to the thickness in the dynamic compression direction when the maximum load is applied in the dynamic compression direction of the rubber composition (the length in the compression deformation direction when the maximum load is applied). For example, in the columnar rubber composition shown in FIG. 1, from the point B to the thickness (length in the compression direction) AB of the rubber composition when the maximum load is applied in the compression direction. It means the movement amount BC of the outermost diameter in torsional deformation displaced to a point, that is, BC / AB.

When the composite deformation is repeatedly applied while gradually increasing the dynamic torsional amplitude, the duration of the dynamic deformation at one dynamic torsional amplitude is 10 seconds or more when the dynamic deformation is stabilized, preferably sufficiently stabilized 30 It is adjusted to be within 10 minutes, more preferably within 5 minutes, taking into consideration the total measurement time, within 1 hour, which does not cause normal fatigue failure such that the rubber specimen is cured. That is, it can be determined that the chipping resistance is excellent if a composite deformation having a dynamic torsional amplitude of 250% or more is applied for a time in the above range and no breakdown occurs.

In the composite deformation, the measurement temperature is 70 to 150 ° C, preferably 90 to 120 ° C. If the temperature is lower than 70 ° C, heat generation during driving cannot be taken into consideration, so the chipping resistance cannot be fully evaluated. If the temperature exceeds 150 ° C, the thermal degradation of the rubber has priority. Can not do it.

The measuring device capable of inputting the composite deformation in the present invention is not particularly limited as long as it can continuously apply dynamic compression deformation and dynamic torsion deformation to the rubber composition, for example, The viscoelasticity measuring device described in JP-A-2006-177734 can be used.

Specifically, compound deformation uses a cylindrical or rectangular parallelepiped-shaped sample fixed between two metal plates placed in parallel with an adhesive as a measurement sample, and the metal plate is used as a measurement jig. After fixing, cyclic deformation of compression and torsion is simultaneously applied between the metal plates, and measurement is performed while increasing the amplitude of torsional deformation until the sample breaks.

The composite deformation will be described more specifically with reference to the drawings.
FIG. 2 is a schematic diagram illustrating an example of the measurement sample 1. The measurement sample 1 includes a cylindrical rubber test piece 11 and a pair of metal plates 12A and 12B. The pair of metal plates 12A and 12B are attached to the circular upper surface 11A and lower surface 11B of the rubber test piece 11, respectively.

The measurement sample 1 shown in FIG. 2 can be set in the above-described apparatus and subjected to complex deformation. Specifically, as shown in FIG. 2, it repeats in the cylinder axis direction (X direction in FIG. 2) with respect to the circular upper surface 11A and lower surface 11B of the rubber test piece 11 via a pair of metal plates 12A and 12B. By inputting the compressive deformation, the dynamic compressive deformation is applied to the rubber test piece 11 from the upper surface 11A and the lower surface 11B. Further, by repeatedly applying torsional deformation to the upper surface 11A in the circumferential direction (T direction in FIG. 2) via the metal plate 12A, the upper surface 11A is repeatedly displaced to the RA point and the RB point around the origin OR (zero displacement). Dynamic torsional deformation is applied.

Since the dynamic compression deformation corresponds to the deformation due to the vehicle weight, and the dynamic torsion deformation corresponds to the deformation received from the road surface during turning, the maximum displacement point of the dynamic compression deformation, that is, the pair of metal plates 12A By synchronizing the time when the distance of 12B becomes the minimum and the maximum displacement point of the dynamic torsional deformation, that is, the time when the dynamic torsional strain angle α is maximized by being twisted most, Deformation can be reproduced well.

Then, while gradually increasing the dynamic torsional amplitude, the dynamic compression deformation and dynamic torsional deformation are continuously input to the rubber test piece 11, and the dynamic torsional amplitude (torsional displacement) at the time of breaking the rubber test piece 11 is measured. By doing so, it is possible to predict chipping resistance when a sample having the same composition as that of the rubber test piece 11 is used for a tire tread, and if it is 250% or more, it can be evaluated that the performance is excellent. “Fracture” refers to “cracking (appearance)” and “reduction in stress (physical properties)”. In this test, the point at which the stress decreases when dynamic torsion is applied is Is determined. For example, by inputting a strain of 150% for 1 minute and increasing the amount of strain in 10% increments until the rubber composition breaks, a compression torsion test is performed. It can be the time when the slope becomes negative in the plot.

In the measurement sample shown in FIG. 2, the material of the metal plates 12A and 12B is not particularly defined, and examples thereof include stainless steel, iron, and brass. The rubber test piece 11 and the metal plates 12A and 12B can be bonded with, for example, a general adhesive (epoxy adhesive, urethane adhesive, vulcanized adhesive, etc.) capable of bonding between metal and rubber. And a technique for adhering a vulcanized sample and a technique for adhering a metal plate and a rubber composition simultaneously with vulcanization. In any method, it is sufficient that peeling between the metal plate and the rubber does not occur until the sample breaks, and thereby, the chipping resistance performance when the measured rubber sample is used for a tire can be evaluated well.

A rubber-metal composite, which is a measurement sample used in the compression torsion test, is a rubber-metal composite having a rubber piece made of the rubber composition of the present invention and a pair of metal plates sandwiching the rubber piece. The rubber piece has a constricted portion, a circumferential notch formed at a position of the minimum diameter of the constricted portion, and a pair of cylindrical portions sandwiching the constricted portion, and the depth of the notch Is preferably 5 to 25% of the minimum diameter of the constricted portion.

The conventional rubber-metal composite has a structure in which a cylindrical rubber test piece 11 is sandwiched between a pair of metal plates 12 as shown in FIG. Then, the adhesion part of the rubber test piece 11 and the metal plate 12 will be destroyed, and the rubber destructive test may not be performed accurately. On the other hand, as shown in FIG. 3, a preferable rubber-metal composite has a constricted portion 1a, a circumferential notch (guideline) 1e formed at the position of the minimum diameter of the constricted portion 1a, and the constricted portion. Since the rubber test piece 11 having a pair of cylindrical portions 1b sandwiching the portion 1a is sandwiched between the pair of metal plates 2, the strain energy is formed at the center (minimum diameter portion) of the constricted portion 1a. It is possible to concentrate on the notch 1e and control the extension direction of the fracture. Thereby, the fracture | rupture of the adhesion part of the sample 1 for a measurement and the metal plate 2 is suppressed, and even under the above severe conditions, a rubber destructive test can be performed accurately and with good reproducibility.

In addition, in this specification, a cylindrical part means the part comprised by the cylinder with a substantially constant diameter, and a constriction part means the part from which each diameter is gradually reduced toward the center from each cylindrical part of a rubber piece. Say. In the case of a rubber piece having no cylindrical part, the constricted part refers to a part where the diameter gradually decreases from the end of the rubber piece toward the center.

The depth of the guide line (e in FIG. 3) is 5% or more, preferably 10% or more of the minimum diameter of the constricted portion. If it is less than 5%, the effect of forming the guideline is weak, and the extension direction of fracture may not be controlled. The depth of the guideline is 25% or less, preferably 15% or less of the minimum diameter of the constricted portion. If it exceeds 25%, the extension direction of the fracture can be controlled, but the rubber breaks with a small strain, which is not preferable as an evaluation method for the fracture test.

The method of inserting the guideline is not particularly limited, but a method of rotating the rubber-metal composite by applying the razor blade 21 to the position of the minimum diameter of the constricted portion of the rubber piece using an apparatus as shown in FIG. According to this method, it is possible to form a circumferential guideline with a uniform depth. Further, by attaching a micrometer 23 to the fixing jig 22 of the razor blade 21, the depth of the guideline can be controlled in units of 0.1 mm.

The minimum diameter of the constricted part (a in FIG. 3) is preferably 30% or more, more preferably 40% or more of the maximum diameter of the cylindrical part. If it is less than 30%, the rubber piece cannot withstand repeated deformation and the rubber destructive test may not be performed accurately. The minimum diameter of the constricted portion of the rubber piece is preferably 70% or less, more preferably 60% or less of the maximum diameter of the cylindrical portion. If it exceeds 70%, the effect of changing the shape of the rubber piece is unlikely to appear, and there is a tendency that almost the same test result as that of a conventionally used columnar rubber piece is obtained.

The height of each cylindrical portion (b in FIG. 3) is preferably 10% or more, and more preferably 15% or more of the total height of the rubber piece. If it is less than 10%, sufficient adhesion between the metal plate and the rubber piece may not be ensured. The height of each columnar part is preferably 30% or less, more preferably 25% or less of the total height of the rubber piece. If it exceeds 30%, the angle of the constricted portion becomes steep, and strain energy tends to be applied to other than the center of the constricted portion, so that the rubber destructive test may not be performed accurately.

In addition, although the height (c of FIG. 3) of the whole rubber piece is not specifically limited, What is necessary is just about 1-1000 mm (preferably 1-100 mm). Similarly, the maximum diameter of the cylindrical portion (d in FIG. 3) may be about 2 to 2000 mm (preferably 2 to 200 mm).

It is preferable that the rubber pieces have a substantially symmetrical shape in the vertical and horizontal directions because the strain energy is easily concentrated at the center of the constricted portion. For the same reason, the position of the minimum diameter of the constricted portion is preferably an intermediate point of the height of the entire rubber piece.

Although it does not specifically limit as a material of a metal plate, For example, iron, steel, lead, aluminum, copper etc. are mentioned.

The rubber-metal composite is produced by a usual method. That is, the rubber composition of the present invention can be produced by processing it into a desired shape at an unvulcanized stage, sandwiching it with a metal plate coated with an adhesive, and heating and pressing in a vulcanizer. it can.

The rubber composition of the present invention preferably contains a rubber component containing a white filler such as carbon black or silica. The compounding amount of carbon black and white filler is preferably 10 to 150 parts by mass, more preferably 30 to 100 parts by mass, and still more preferably 45 to 80 parts by mass with respect to 100 parts by mass of the rubber component.

Examples of rubber components include modified natural rubber such as natural rubber (NR) and epoxidized natural rubber (ENR), isoprene rubber (IR), butadiene rubber (BR), styrene butadiene rubber (SBR), and butyl rubber (IIR). Brominated product of isobutylene-p-methylstyrene copolymer, acrylonitrile-butadiene rubber (NBR), chloroprene rubber (CR), ethylene-propylene rubber (EPM), ethylene-propylene-diene copolymer rubber (EPDM), styrene- Isoprene rubber, styrene-isoprene-butadiene rubber copolymer rubber (SIBR), isoprene-butadiene rubber, chlorosulfonated polyethylene (CSM), acrylic rubber (ACM, ANM), epichlorohydrin rubber (CO, ECO, GECO), polysulfide rubber (T), Silico Rubber (Q), fluorine rubber (FKM), and the like urethane rubber (U). These may be used alone or in combination of two or more.

Carbon black includes furnace black, acetylene black, thermal black, channel black, graphite and the like, and specific examples include SAF-HS, SAF, ISAF, ISAF-HS, ISAF-LS, IISAF-HS, HAF, There are HAF-HS, HAF-LS, FEF, GPF, SRF and the like. These carbon blacks can be used alone or in combination of two or more.

The compounding amount of carbon black is preferably 10 to 150 parts by mass with respect to 100 parts by mass of the rubber component. If the amount is less than 10 parts by mass, sufficient reinforcing property tends not to be obtained. If the amount exceeds 150 parts by mass, heat generation increases and rolling resistance deteriorates, workability deteriorates, and the reinforcement property may decrease. There is. The blending amount is more preferably 30 to 100 parts by mass, and further preferably 45 to 80 parts by mass.

Silica can be appropriately selected and used from those conventionally used for reinforcing rubber, for example, dry silica, wet silica, etc. Among them, wet silica is preferable. Preferable examples of the wet process silica include Degussa Ultrasil VN3, Tosoh Silica Co., Ltd. nip seal AQ, and the like.

The amount of silica is preferably 5 parts by mass or more with respect to 100 parts by mass of the rubber component. When the amount is less than 5 parts by mass, it is difficult to obtain a rolling resistance reduction effect and a wet grip improvement effect by using silica. The amount is preferably 150 parts by mass or less, more preferably 80 parts by mass or less. When it exceeds 150 mass parts, there exists a tendency for workability to fall.

When silica is blended, it is desirable to further add a silane coupling agent. It does not specifically limit as a silane coupling agent, The general thing used conventionally can be used.

0.5-20 mass parts is preferable with respect to 100 mass parts of silica, and, as for the compounding quantity of a silane coupling agent, 2.5-10 mass parts is more preferable. If the amount is less than 0.5 parts by mass, the effect of improving the dispersion of silica by adding a silane coupling agent cannot be obtained sufficiently, and the wear resistance and fracture energy tend to decrease. However, there is a case where the effect is not obtained for the increase of the resistance, and further, the reinforcement property and the wear resistance are deteriorated.

The rubber composition of the present invention may contain a softening agent. Softeners include paraffinic process oil, naphthenic process oil, aromatic process oil, castor oil, cottonseed oil, linseed oil, rapeseed oil, soybean oil, palm oil, palm oil, peanut water, rosin, Examples include vegetable oils such as pine oil, pine tar, tall oil, corn oil, rice bran oil, ben flower oil, sesame oil, olive oil, sunflower oil, palm kernel oil, coconut oil, jojoba oil, macadamia nut oil, safflower oil, tung oil, etc. . What is necessary is just to select the compounding quantity of a softening agent suitably.

The rubber composition of the present invention may be blended with an anti-aging agent, and is particularly limited as long as it is usually used in rubber compositions such as a heat-resistant anti-aging agent and a weather-resistant anti-aging agent. Can be used without Specifically, naphthylamine type (phenyl-α-naphthylamine etc.), diphenylamine type (octylated diphenylamine, 4,4'-bis (α, α'-dimethylbenzyl) diphenylamine etc.), p-phenylenediamine type (N- Isopropyl-N'-phenyl-p-phenylenediamine, N- (1,3-dimethylbutyl) -N'-phenyl-p-phenylenediamine, N, N'-di-2-naphthyl-p-phenylenediamine, etc.) Amine-based anti-aging agents such as 2,2,4-trimethyl-1,2-dihydroquinoline and other quinoline anti-aging agents; monophenol-based (2,6-di-t-butyl-4-methyl) Phenol, styrenated phenol, etc.), bis, tris, polyphenol (tetrakis- [methylene-3- (3 ', 5'-di-t-butyl) Le-4'-hydroxyphenyl) propionate] methane) phenolic antioxidant, and the like. What is necessary is just to select the compounding quantity of an anti-aging agent suitably.

In addition to the above components, the rubber composition contains a compounding agent conventionally used in the rubber industry, for example, a crosslinking agent such as an antioxidant, zinc oxide, sulfur, and a sulfur-containing compound, a vulcanization accelerator, and the like. May be. 0.5-5 mass parts is preferable with respect to 100 mass parts of rubber components, as for the compounding quantity of a crosslinking agent, 1-3 mass parts is more preferable, and 1.5-2.5 mass parts is still more preferable. If the amount is less than 0.5 parts by mass, the wear resistance tends to decrease. If the amount exceeds 5 parts by mass, the rubber tends to be extremely hard and the grip performance tends to decrease.

The tire rubber composition of the present invention is produced by a general method. That is, it can be produced by a method of kneading each component with a kneader such as a Banbury mixer, a kneader, or an open roll, and then vulcanizing.

The rubber composition for tires of the present invention is preferably used for a tread. A pneumatic tire produced by using the tire rubber composition for a tread is produced by a usual method. That is, the rubber composition containing the above components is extruded in accordance with the shape of the tread at an unvulcanized stage and molded together with other tire members on a tire molding machine by a normal method. Form a vulcanized tire. A pneumatic tire can be manufactured by heating and pressing the unvulcanized tire in a vulcanizer.

By inputting complex deformation, it is difficult to discriminate chipping resistance in conventional uniaxial tensile tests, but it is possible to compare formulations with differences in market performance according to the order of market performance. Accordingly, since the order of market performance can be relatively determined based on the criterion that the dynamic torsion amplitude in the present invention is not less than a predetermined value, a tread portion having excellent chipping resistance can be provided.

The present invention also relates to a method for destructive testing of a crosslinked rubber body in which combined deformation of dynamic compression deformation and dynamic torsion deformation is simultaneously applied to a sample at 70 to 150 ° C. By giving the rubber test piece a compression torsion mode that is input to the running tire, the tread chipping that occurs in the tire can be reproduced in the laboratory. At this time, when the rubber test piece is brought to a high temperature state, the evaluation is performed under more severe conditions, and the superiority and inferiority of the tread chipping resistance performance appears remarkably.

The present invention will be specifically described based on examples, but the present invention is not limited to these examples.

The various chemicals used in the examples and comparative examples are described in detail below.
Natural rubber (NR): TSR20
Butadiene rubber (BR): BR150B manufactured by Ube Industries, Ltd.
Carbon Black N330: Show Black N220 (N ₂ SA: 175 m ² / g) manufactured by Cabot Japan
Silica: Ultrasil VN3 (Nitrogen adsorption specific surface area (N ₂ SA): 175 m ² / g) manufactured by Tegusa
Silane coupling agent: Si69 (bis (3-triethoxysilylpropyl) tetrasulfide) manufactured by Tegussa
Phenylenediamine-based anti-aging agent: NOCRACK 6C (N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine) manufactured by Ouchi Shinsei Chemical Co., Ltd.
Wax: Ozoace 0355 manufactured by Nippon Seiwa Co., Ltd.
Zinc oxide: 2 types of zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd. Stearic acid: Agate powder sulfur manufactured by NOF Corporation (containing 5% oil): 5% oil treated powder sulfur manufactured by Tsurumi Chemical Co., Ltd. ( Soluble sulfur containing 5% oil by weight)
Vulcanization accelerator: Noxeller NS (N-tert-butyl-2-benzothiazylsulfenamide) manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.

(Examples 1-3 and Comparative Examples 1-2)
According to the formulation shown in Table 1 (the numerical values of various chemicals in the table indicate parts by mass), using a 1.7 L Banbury mixer manufactured by Kobe Steel Co., Ltd., other than sulfur, vulcanizing agent and vulcanization accelerator Were kneaded for 5 minutes at 150 ° C. to obtain a kneaded product (step 1). Next, sulfur, a vulcanizing agent, and a vulcanization accelerator were added to the kneaded material obtained, and kneaded for 5 minutes at 80 ° C. using an open roll to obtain an unvulcanized rubber composition ( Step 2).

A rubber composition was obtained by vulcanizing at 160 ° C. for 20 minutes using a mold that is a rubber having a constriction having a height of 10 mm, a maximum diameter of 20 mm, and a minimum diameter of 10 mm (center portion in the height direction).

<Tread chip resistance>
Evaluation was made by the following method described in JP2012-251833A. The hitting piece of the pendulum provided with the hitting piece at the tip of the arm collided with the front surface of the rubber test piece, and the fracture energy was calculated from the pendulum drop energy and the state of the rubber test piece lacking rubber using the following formula. .
(Fracture energy) = (Tensile strength) × (Elongation at cutting) / 2
(Test equipment)
・ Pendulum arm length = 450mm
・ Weight of striking piece = 300g
・ Swing angle α = 90 °
・ Size of the striking piece main body (cuboid: height = 29 mm, depth = 29 mm, width 39 in the axis i direction)
・ Angle of lower corner Q: θ = 90 °
(Rubber specimen)
・ Size of rubber test piece (cuboid: height HB = 24 mm, depth HA = 39 mm, width W in the direction of the axis i = 59 mm)
・ Size of notch (vertical depth Hb = 7.0 mm, lateral depth Ha = 7.0 mm, notch width t = 0.2 mm)
・ Incision interval = 13 mm
(Collision situation)
-Collision with T2 immediately after passing the vertical line (L = 2.0mm)
-Collision (line contact) at lower corner Q
・ Collision height Hp = 3.5mm (0.5 × Hb)
・ Number of notches arranged in the collision range = 3 (warming condition)
・ Temperature = 80 ℃
(Evaluation criteria)
The weight of the rubber chipped in the tread chipping test was measured, and the rubber composition shown in Example 1 was set to 100, and the tread chipping performance was evaluated based on the following criteria. The smaller the index, the better the tread resistance. In addition, the rubber composition of Example 1 produces a pneumatic tire (size: 11R22.5) adopted as a tread rubber, and is excellent in tread chipping resistance with less tread chipping in appearance evaluation by actual vehicle running on the market. The result is obtained.
○: Index is 100 or less ×: Index exceeds 100

<Strain at fracture in compression torsion test (dynamic compression deformation and dynamic torsion deformation)>
The evaluation of tread chipping resistance was performed under the following conditions using a large fatigue tester manufactured by Yoshimizu Corporation.
Strain input: Compression torsion mode load: 1 MPa
Strain input frequency: 10 Hz
Number of strain inputs: 600 times Strain amount: Input in increments of 10% from 150% (150%, 160%, 170%, ...)
(A constant strain amount is repeatedly input 600 times. If no fracture occurs, the strain is further increased by 10%.)
Test temperature: 100 ° C. (Test is performed after holding at 100 ° C. for 3 hours)
It implemented by n = 3 with respect to each test piece produced from the composition of Examples 1-3 and Comparative Examples 1-2, and calculated the average value. Table 2 shows the results.

<Tensile test>
The tensile test was performed according to JIS K-6251 with n = 3, and the average value was calculated. Table 2 shows the results.

In the tires produced in Examples 1 to 3, no tread chipping occurs and the mechanical strength is excellent. However, in the tires produced in Comparative Examples 1 to 2, tread chipping occurs and the mechanical strength is poor.
When the elongation at break (EB) in the uniaxial tensile test at room temperature was performed, the test pieces obtained from the rubber compositions of Examples 1 and 2 and Comparative Example 1 exceeded 500%. The test piece obtained from the rubber composition of Comparative Example 2 is less than 500%, and cannot show the superiority or inferiority of the tread chipping in the tire.

On the other hand, when a compression torsion test was performed at a high temperature, the test pieces prepared in Examples 1 to 3 had a strain at break of 250% or more, and the test pieces prepared in Comparative Examples 1 and 2 had strain at break. The amount was less than 250%. By using the test method of the present invention as a guideline, it is possible to provide a rubber composition and a pneumatic tire excellent in tread resistance.

1 Measurement Sample 1a: Constriction 1b: Column 1e: Cut (Guideline)
DESCRIPTION OF SYMBOLS 11 Rubber test piece 11A Circular upper surface 11B of rubber test piece Circular lower surface 12A, 12B of rubber test piece Metal plate 2, 12: Metal plate 21: Razor blade 22: Fixing jig 23: Micrometer a: Constriction Minimum diameter b: height of cylindrical portion c: height of entire rubber piece d: maximum diameter of cylindrical portion e: depth of guideline

Claims (7)

A rubber composition for a tire that is destroyed at a dynamic torsional amplitude of 250% or more when a dynamic torsional deformation synchronized with the compressive strain is applied during the dynamic compressive deformation at 70 to 150 ° C. The tire rubber composition according to claim 1, wherein the compressive load of dynamic compression deformation is 50 kPa to 10 MPa. The rubber composition for tires according to claim 1 or 2, wherein the cycle of dynamic compression deformation is 1 to 100 Hz. The rubber composition for tire according to any one of claims 1 to 3, comprising 10 to 150 parts by mass of carbon black or white filler with respect to 100 parts by weight of the diene rubber component. Furthermore, 0.5-5 mass parts of crosslinking agents are contained with respect to 100 weight part of diene-type rubber components, The rubber composition for tires of Claim 4 characterized by the above-mentioned. The pneumatic tire produced using the rubber composition for tires in any one of Claims 1-5. A fracture test method for a crosslinked rubber body, comprising a step of simultaneously applying a composite deformation of dynamic compression deformation and dynamic torsion deformation to a sample at 70 to 150 ° C.

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