JP2002019416A - Pneumatic studless tire for heavy load - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic studless tire for a heavy load for improving on-ice performance and abrasion resistance by a structure of a tread part. SOLUTION: In this pneumatic studless tire for the heavy load, the tread part is composed of a three-layer structure of a cap A, a cap B and a base C, the tread part is provided so that the groove bottoms are positioned in an A layer, the gauge ratio of the A layer/a B layer/a C layer in a shoulder part and a crown center part is 35 to 80/60 to 20/2 to 20 (total 100%), the C layer is positioned below a line connecting the respective groove bottoms in the crown center part from the tire shoulder part, the A layer is NR/BR=40 to 80/60 to 20 (the wt.% ratio) (total 100%), the B layer is NR/BR=60 to 100/40 to 0 (the wt.% ratio) (total 100%), the C layer is composed of NR and/or IR, and the total blending quantity of a softener and/or a plasticizer in the A layer, the B layer and the C layer satisfies the relationship of a blending quantity (here, a blending quantity in the C layer is substantially 0) of a blending quantity in the A layer > a blending quantity in the B layer >= a blending quantity in the C layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pneumatic studless tire for heavy loads, and more particularly to a pneumatic studless tire for heavy loads having a three-layered tread and improved on-ice performance and abrasion resistance.

[0002]

2. Description of the Related Art In recent years, in heavy duty tires, natural rubber (NR) alone or NR has been used for the purpose of improving wear resistance.
/ A cap in which ultrafine carbon black is blended with a polybutadiene rubber (BR) blend is often used in a tread portion. However, it is difficult to achieve both opposing performances such as compatibility between abrasion resistance and durability, and compatibility between on-ice performance and abrasion resistance with a single-layer tread. Many patent applications have been proposed for their formulation and structure. However, in the tread having the structure, if the performance is to be further improved, there is a concern that the workability at the time of molding may be deteriorated or the adhesion to the belt portion may be deteriorated.

[0003] As a tread portion having a three-layer structure, for example, Japanese Unexamined Patent Application Publication No. 11-60810 discloses a heavy-duty tire in which a tread portion having a three-layer structure is used to improve wear resistance, heat durability and wandering resistance. Has been described. Japanese Patent Application Laid-Open No. 6-8708 describes a studless tire in which the on-ice performance after the middle stage of wear is improved by using a rubber layer having a higher foaming ratio as the inner layer of the tread portion having a three-layer structure.

[0004]

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a pneumatic studless tire for heavy loads which has improved both on-ice performance and abrasion resistance in view of the above-mentioned state of the art.

[0005]

According to the present invention, the tread portion is composed of the cap-A, the cap-B and the base-C.
In a heavy-duty pneumatic studless tire having a tread portion having a layer structure and having a groove bottom located in a cap-A layer, a gauge ratio of A layer / B layer / C layer at a shoulder portion and a crown center portion is 35 to 50%. 80 / 60-2
0/2 to 20 (total of 100%), the base-C layer is located below the line connecting the groove bottoms from the tire shoulder portion to the crown center portion (that is, even if the base is used up to the groove bottom). -C layer is not exposed), Cap-A layer is natural rubber (NR) / polybutadiene rubber (BR) = 40
~ 80/60 ~ 20 (weight% ratio) (total 100%)
Cap-B layer has NR / BR = 60-100 / 40-0
(% By weight) (total 100%), base-C is N
R and / or polyisoprene rubber (IR), and the total blending amount of the softener and / or plasticizer in the cap-A layer, the cap-B layer and the base-C layer is in the cap-A layer. A pneumatic studless tire for heavy load is provided that satisfies the relationship of: compounding amount> capping amount in B-layer ≧ compounding amount in the base-C layer (however, the compounding amount in the base-C layer is substantially zero). Is done.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted research to solve the problem of maintaining the wear resistance and durability while improving the performance on ice, which is a problem in heavy duty tires. Uses a tread with a layered structure, the first layer uses a compound that emphasizes performance on ice, the second layer uses a compound that is resistant to abrasion, and the third layer uses a compound that prevents oil migration and has high adhesiveness. By arranging them and defining these gauge ratios, a studless tire for heavy load that achieved the above object was successfully obtained. This will be further described below.

As shown in FIG. 1, a pneumatic studless tire for heavy load according to the present invention has a tread portion 1 having a cap-A layer 2, a cap-B layer 3 and a base-C layer 4-3.
It has a layered structure and has three layers A, B and C as described below.
The object has been achieved by specifying the gauge thickness of the shoulder portion 5 and the crown center portion 6 of the layer and the mixing ratio of the softener / plasticizer together with the constituent rubbers of A, B and C. As shown in FIG. 1, the groove bottom 7 of the tread portion 1 of the pneumatic studless tire according to the present invention is located in the cap-A layer 2.

[0008] The rubber constituting the A, B and C layers of the tread portion of the pneumatic studless tire according to the present invention is a natural rubber (NR) or a polyisoprene rubber which has been generally compounded in a rubber composition for a tire. (IR), various styrene-butadiene copolymer rubbers (SBR), and various polybutadiene rubbers (BR) can be used alone or as an arbitrary blend.

[0009] In the pneumatic studless tire according to the present invention, the gauge ratio of the A layer / B layer / C layer at the shoulder portion and the crown center portion of the tread portion is 35 to 80 /.
It should be 60 to 20/2 to 20 (total of 100%), preferably 40 to 70/50 to 30/2 to 15, respectively.

The cap-A layer in the tread portion of the pneumatic studless tire according to the present invention has NR / BR = 40-8.
0/60 to 20 (weight% ratio) (100% in total, preferably NR / BR = 50 to 80/50 to 20).

The cap-B layer in the tread portion of the pneumatic studless tire according to the present invention has NR / BR = 60 to 1
00 / 40-0 and the base-C layer is composed of NR and / or IR (preferably NR alone).

Conventionally known softeners (for example, various process oils, aromatic oils, paraffinic oils, etc.) to be added to each of the layers A, B and C of the tread portion of the pneumatic studless tire according to the present invention and / or Alternatively, when a plasticizer (for example, dioctyl sebacate (DOS)) is blended, the following relationship must be satisfied.
Compounding amount in Cap-A layer> Compounding amount in Cap-B layer ≧ Compounding amount in base-C layer (however, the compounding amount in Base-C layer is substantially zero.)

If the amount of the compound in the cap-B layer is larger than the amount of the compound in the cap-A layer, it is not preferable because sufficient hardness on ice and snow cannot be ensured particularly due to an increase in hardness at a low temperature.

In the layers A, B and C of the present invention, carbon black can be blended with the above rubber. As the carbon black used in the present invention, carbon black conventionally used in pneumatic studless tires for heavy loads can be used.

In the rubber composition constituting the A, B and C layers of the tread portion of the pneumatic studless tire according to the present invention, in addition to the above-mentioned essential components, a reinforcing agent (filler) such as silica, a vulcanization accelerator. Agents, antioxidants, etc., can be blended with various additives that are generally blended for pneumatic tires, and such a blend is kneaded and vulcanized into a composition by a general method. Can be vulcanized. As long as the amount of these additives is not contrary to the object of the present invention,
A conventional general compounding amount can be used.

[0016]

EXAMPLES Hereinafter, the present invention will be further described with reference to Examples, but it goes without saying that the scope of the present invention is not limited to these Examples. Examples 1 and 2 and Comparative Examples 1 to 5 Tread layers A-1 or A-2, B-1 having the structure shown in Table I
Alternatively, B-2 and C-1 or C-2 layers were prepared. The rubber and carbon black used are as follows. NR: Natural rubber (RSS No. 3) BR: BR Nipol BR1220 made by Nippon Zeon Carbon black ISAF: Show black N220 made by Showa Cabot Carbon black SAF: Tokai carbon made seam 9

The following additives were commonly blended in the rubber compositions constituting each of the tread constituent layers A-1 to C-2 (the blending amounts are parts by weight per 100 parts by weight of rubber). Ingredients Amounts zinc white (JIS 3 No.) 4 Oil (manufactured by Idemitsu Kosan Co. Diana Process AH-20) variable industrial stearate 3 Antioxidant 6PPD (N-phenyl--N'-1,3-dimethylbutyl -p- phenylene Diamine) 2.0 Powdered sulfur 1.9 Vulcanization accelerator CBS (N-cyclohexyl-2-benzothiazolesulfenamide) 1.2

Preparation of Sample In the formulation shown in Table I, the vulcanization accelerator and components other than sulfur were kneaded in a 1.8-liter closed mixer for 3 to 5 minutes, and released when the temperature reached 165 ± 5 ° C. A master batch was obtained. 8 vulcanization accelerator and sulfur
An inch open roll was kneaded to obtain a rubber composition. Next, the composition was placed in a mold of 15 × 15 × 0.2 cm for 16 hours.
The target test piece (rubber sheet) was prepared by press vulcanization at 0 ° C. for 20 minutes, and the vulcanization properties were evaluated. The results are shown in Table I.

The test methods for the physical properties of the compositions obtained in the examples are as follows. Performance index on ice: Skid resistance on ice was measured on an ice plate at an ice temperature of −3 ° C. using a British pendulum tester. The value of the tread A-1 was shown as an index value at 100 ° C. (the performance on ice was higher). Wear resistance index: Using a Lambourn abrasion tester (manufactured by Iwamoto Seisakusho Co., Ltd.), load 5 kg, slip rate 25%,
The wear loss measured under the conditions of a time of 4 minutes and room temperature was shown as an index (the larger the number, the better the wear resistance).

[0020]

[Table 1]

Next, a tire tread portion having a three-layer structure was manufactured by using the rubber compositions A-1 to C-2 for tire tread obtained above in combinations and gauge ratios shown in Table II. The manufacturing method is as follows. It was carried out in one piece extrusion using a three-color extruder. However, either A / B / C can be individually extruded and then compression molded, or A / B integral extrusion (or A alone extrusion) and A single extrusion (or B / C integral extrusion) can be both compression molded.

[0022]

[Table 2]

[0023]

[Table 3]

The physical properties of the obtained three-layer tire tread were evaluated by the following methods, and the results are shown in Table II. On-ice performance index: The above-mentioned on-ice performance index of the tread exposed at the time of the remaining groove of 50% was substituted (largely good). Tread abrasion index: The sum of the product of the gauge ratio and the aforementioned abrasion resistance index in each of A / B / C occupying the tread positioned above the groove bottom was defined as the tread abrasion resistance index ( The better the better).

Chipping resistance: The surface condition at 15% of the tread residual groove from the groove bottom was visually checked, and the quality of chipping resistance was judged based on the size of chipping (tipping) in the tread portion. Evaluation criteria: ○: no chipping to small (chip 0 to 1 mm) △: chipping (chip 1 to 2 mm) ×: large chipping (chip more than 2 mm) Molding workability: The tread was molded and used 3 days after the extrusion date. In the work of winding the tread on the forming drum, the quality of the forming workability was judged from the presence or absence of peeling of the tread tip. Evaluation criteria:…: No peeling off without applying rubber volatile oil. Δ: No peeling off due to rubber volatile oil application. ×: Peeled off by wire brushing in addition to rubber volatile oil application. Migration prevention: 3mm tread remaining groove from groove bottom
The rubber covering the outer layer of the steel belt located at the outermost layer of the tire at the time was sampled, and the weight percentage of the component extracted with acetone was determined in accordance with JIS K6229. The difference in the weight percentage of the acetone-extracted component of the clothing rubber when new was measured in advance was defined as the amount of oil migration. Evaluation criteria:…: difference in measurement error (less than 1%) Δ: difference: 1 to 2% ×: difference: more than 2% Calf cracking property: The occurrence of cracks between tread kerfs at the time of 3 mm remaining groove was measured. Evaluation criteria: ○… No or 2mm or less ×… Yes

[0026]

As described above, the pneumatic studless tire for heavy load according to the present invention runs on the cap rubber layer A emphasizing performance on ice at least up to the platform where performance on ice is emphasized, and the NR / BR The blend also has an effect of preventing calf cracking, and the wear resistance after the middle stage of wear and the chipping resistance at the end stage are secured by the cap rubber layer B in the tread portion. In the rubber layer A, a softener / plasticizer can be blended to reduce the hardness. However, the rubber layer B should be less than the rubber layer A, and the blending amount of the rubber layer C should be substantially zero. Thereby, a decrease in durability due to migration of the softener to the steel belt layer can be prevented. In the present invention, the rubber layers A and B made of natural rubber / polybutadiene rubber ensure abrasion resistance (the rubber layer A prevents cracks at the groove bottom), and the rubber layer C made of natural rubber (or polyisoprene rubber) is used. Adhesion to the tack and steel belt layers can be ensured.

[Brief description of the drawings]

FIG. 1 is a drawing showing an example of the structure of a tread portion of a heavy-duty pneumatic studless tire according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Tread part 2 ... Cap-A layer 3 ... Cap-B layer 4 ... Base-C layer 5 ... Shoulder part 6 ... Crown center part 7 ... Groove bottom

Claims (1)

[Claims] 1. The tread portion has a cap-A, a cap-
B and a base-C having a three-layer structure, and a cap-
In a heavy-duty pneumatic studless tire having a tread portion in which a groove bottom is located in the A layer, the gauge ratio of the A layer / B layer / C layer in the shoulder portion and the crown center portion is 35 to 80/60 to 20/2 to 2. 20
(Total 100%), the base-C layer is located below the line connecting the groove bottoms from the tire shoulder portion to the crown center portion, and the cap-A layer is made of natural rubber (N
R) / polybutadiene rubber (BR) = 40-80 / 60
~ 20 (weight% ratio) (100% in total), Cap-B
The layer is NR / BR = 60-100 / 40-0 (weight% ratio)
The base-C is composed of NR and / or polyisoprene rubber (IR), and the softener and / or plasticizer in the cap-A layer, the cap-B layer and the base-C layer. Cap-A
Amount in layer> Amount in cap-B layer ≧ Base-C
A pneumatic studless tire for heavy loads that satisfies the relationship of the compounding amount in the layer (however, the compounding amount in the base-C layer is substantially zero).