JPH0115404B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a tread rubber composition for tires for heavy-duty vehicles, and more specifically, it has good braking performance on snow and ice roads and good braking performance on wet roads, and has good wear resistance and cut chipping resistance as tires for general road use, especially lug tires. The present invention relates to a tread rubber composition for heavy-duty vehicle tires used for relatively large vehicles such as trucks and buses, which has excellent performance. Traditionally, tires used for relatively large vehicles such as trucks and buses (hereinafter referred to as truck and bus tires) are winter tires, so-called snow tires, that have excellent braking performance on snow and ice roads (hereinafter referred to as ice skid properties). General road tires, which have excellent wear resistance and braking performance on wet road surfaces (hereinafter referred to as wet skid properties), have been used depending on the season. That is, in the prior art, tread rubber compositions for winter tires such as snow tires used on snow and ice roads and tread rubber compositions for general road tires used on wet roads have different performances as described above. Because of the requirements, it has been common practice to use different rubber compositions. Therefore, users in icy and snowy areas have had to accept the inconvenience of having to use two types of tires, snow tires and regular tires, depending on their needs. In the end, imparting ice skid properties to a treaded rubber that has wear resistance and wet skid properties results in a decrease in performance in terms of wet skid properties and handling stability, and it has been difficult to obtain a tread rubber that satisfies both properties. In addition, in order to compensate for these deficiencies in tread rubber, attempts have been made to create an all-weather block pattern as a tread pattern, and chains have been installed on general road tires to drive on ice and snow.
The former causes a decrease in wear resistance and noise problems, while the latter not only damages the road surface but also exacerbates the noise problem, and is extremely dangerous in terms of safety when attaching and detaching on public roads. In addition to this, there is a risk that the chain may cause damage to the tread rubber. Therefore, in addition to abrasion resistance and wet skidding properties for general road tires, this rubber also has the cut resistance, chipping resistance, and fatigue resistance required for relatively large vehicles such as trucks and buses, and has excellent ice skidding properties. What is desired is a material and a pneumatic tire having the rubber material. Therefore, several methods have been proposed for adding ice skid properties to treaded rubber which has excellent properties such as abrasion resistance and wet skid properties, but satisfactory results have not yet been obtained. For example, a method of adding a sodium alginate affinity imparting agent to a rubber composition for toreading (for example,
No. 52-152003) or a method of blending a specific powdered rubber into a rubber composition for toreading (for example,
In the treaded rubber obtained from No. 133248), when ice skid properties are added, the wet skid properties are significantly reduced. In addition, as a method of improving the composition ratio of raw rubber,
For example, JP-A-55-135149, JP-A-55-18388
No., Japanese Patent Publication No. 54-50546, etc.). However, JP-A-55-135149 proposes blending a large amount of styrene-butadiene copolymer rubber (SBR) and extender oil, but the amount of carbon black and extender oil is too large. It is unsuitable for use in truck and bus tires because there is a risk of sagging of the rubber (smashing phenomenon) and peeling of the treaded rubber due to heat generation when overloaded. In addition, the compound mainly composed of natural rubber disclosed in JP-A-55-18388 has poor chipping resistance when used in tires for rough roads, especially lug tires, and is disclosed in JP-A-54-50546. The disclosed formulations in which natural rubber and SBR are the main rubbers do not necessarily provide a satisfactory balance between ice skid properties and wet skid properties. As mentioned above, pneumatic tires used for trucks and buses that have excellent performance in all aspects, such as ice skid properties, wet skid properties, abrasion resistance, and cut chipping resistance, have not yet been developed. It is. The object of the present invention is to meet these demands by satisfying both ice skid properties and wet skid properties, which were conventionally thought to be contradictory, and to provide wear resistance and cut chipping resistance as a tire for rough road surfaces, especially as a lug tire. It is an object of the present invention to provide a tread rubber composition for heavy-duty vehicle tires that also satisfies the following conditions and particularly satisfies the severe conditions required for truck and bus tires. In line with the above objectives, the present inventor has investigated the blending ratio of natural rubber (NR) and/or polyisoprene rubber (IR), styrene-butadiene copolymer rubber (SBR), and polybutadiene rubber (BR), and in particular the characteristics of SBR. In addition to considering the blending ratio to make the most of the properties, we also focused on the characteristics of the extender oil and conducted intensive research. By using an extender oil that is fluid even at low temperatures at a specific blending ratio, the viscoelasticity of vulcanized rubber can be improved. The present invention was achieved by discovering that the decrease can be suppressed. That is, the present invention provides a method for reducing viscosity based on 100 parts by weight of rubber consisting of 30 to 60 parts by weight of natural rubber and/or polyisoprene rubber, 5 to 40 parts by weight of polybutadiene rubber, and 30 to 60 parts by weight of styrene-butadiene copolymer rubber. A tread rubber composition for heavy duty vehicle tires, which contains 5 to 20 parts by weight of an extender oil having a specific gravity constant (VGC) of 0.80 to 0.93 and 45 to 60 parts by weight of carbon black, the tread rubber composition satisfying the above object. It is something to do. Styrene-butadiene copolymer rubber is an essential component for ensuring the handling stability and wet skidding properties of tires for general road surfaces, as well as the cut-chipping resistance required for tires for rough roads (especially lug tires). The blending ratio is 30 to 60 parts by weight in the rubber component. If it exceeds 60 parts by weight, not only the ice skidding property will be reduced, but also the heat generation will increase and tread separation will be induced, and if it is less than 30 parts by weight, the wet skidding property will be poor. The styrene content is preferably 25% by weight or less, particularly preferably 18% by weight or less. If the styrene content is too high, the cut chipping resistance will improve, but the ice skid resistance will decrease. Polybutadiene rubber improves abrasion resistance and ice skid properties, but when added in large amounts,
It induces a decrease in physical properties of breaking strength and tear properties, and also significantly decreases cut chipping resistance.On the other hand, if it is too small, ice skid properties are significantly decreased. Therefore, the blending ratio of the polybutadiene rubber used in the present invention is 5 to 40 parts by weight, preferably 10 to 40 parts by weight, based on the rubber content. Natural rubber and/or polyisoprene rubber has a better balance between wet skid properties and ice skid properties than other polymer components, but if it exceeds 60 parts by weight, the wet skid properties and ice skid properties may be poor even though the physical properties of the vulcanized rubber are satisfactory. It leads to a decline in sexuality. If it is less than 30 parts by weight, in tires that are subjected to relatively large loads such as trucks and buses,
Unsatisfactory due to deterioration in separation properties and physical properties. Therefore, the blending amount is 30 to 60 parts by weight based on the rubber content. In the present invention, a specific viscosity specific gravity constant (V.
It is important to specify the blending ratio of extender oil with GC). It is known to incorporate a large amount of extender oil in order to improve wet skidding properties. However, if it is added in too large a quantity, the extension oil will migrate from the tread to other parts of the tire (so-called oil migration), reducing the adhesion between other reinforcing materials and rubber, and impairing the physical properties of the rubber itself. This causes a change in hardness, a decrease in embrittlement properties (increase in embrittlement temperature), and is therefore unsuitable for use in truck and bus tires that are used for long periods of time. However, by using an extender oil having a viscosity specific gravity constant specified in the present invention in the rubber composition of the present invention, a tread rubber composition for passenger car tires (30 to 80 parts by weight)
It is possible to improve both wet skid properties and ice skid properties while suppressing changes in hardness and deterioration of embrittlement properties of the rubber after vulcanization with a significantly lower blending amount than that of vulcanized rubber. That is, the blending ratio of the extender oil in the present invention is 5 to 20 parts by weight per 100 parts by weight of the rubber content. If it exceeds 20 parts by weight, the strength of the physical properties of the vulcanized rubber decreases, cutting and chipping properties decrease, and the smashing phenomenon (tire tread becomes smaller due to permanent deformation of the rubber) occurs, resulting in poor wear resistance. Wet skid properties and ice skid properties are reduced. On the other hand, if the amount is less than 5 parts by weight, even though the physical properties of the vulcanized rubber are improved, wet skid properties and ice skid properties are deteriorated, and the processability of the rubber is deteriorated. Further, the extender oil used in the present invention is 30 to 80% by weight, preferably 40 to 80% by weight, based on the total amount of extender oil including that already contained in the oil-extended rubber.
The extension oil has a viscosity specific gravity constant (VGC) of 0.80~
in the range of 0.90, and the pour point is -5℃ or less,
It is preferable to use a hydrocarbon oil such as a softener for petroleum-based rubber, which preferably has a temperature of −10° C. or lower. Therefore, the viscosity specific gravity constant (VGC) of the fully extended oil calculated by the following formula (1) is 0.80 to 0.93, preferably
It needs to be between 0.80 and 0.92. Viscosity specific gravity constant (VGC) = 0.00743C _P +0.00925C _N
+0.0110C _A ...(1) (C _P , C _N and C _A represent the paraffin carbon percentage, naphthenic carbon percentage, and aromatic percentage, respectively) Aromatic oils, such as those with VGC 0.96, cannot satisfy the ice skid property. , paraffinic oils such as VGC 0.84 alone or in combination with aromatic oils are essential to achieve the objective. If it is less than 0.80, the wet skid property will not be satisfactory, and furthermore, the compatibility with the rubber will decrease, and the physical properties of the rubber will deteriorate. The carbon black used in the present invention has a rubber content.
The amount is 45 to 60 parts by weight per 100 parts by weight. Carbon black improves wet skid properties, abrasion resistance, and cut resistance, but if it is added in an amount exceeding 70 parts by weight, it not only causes a decrease in cut chipping resistance and abrasion resistance, but also significantly reduces ice skid properties. undesirable;
Further, if the amount is less than 45 parts by weight, it is also undesirable because the wear resistance decreases. In addition, in the rubber composition of the present invention, in addition to the above-mentioned rubber component, extender oil, and carbon black, zinc oxide, stearic acid, an antiaging agent, wax,
Compounding agents such as a vulcanization accelerator and sulfur are blended in appropriate amounts. The present invention will be specifically explained below with reference to Examples and Comparative Examples. All formulations in the table are parts by weight. Examples 1 to 5 and Comparative Examples 1 to 2 Rubber compositions were prepared by mixing rubber components and various compounding agents in a B-type Banbury mixer for 4 minutes according to the formulations shown in Table 1. This rubber composition was vulcanized at 148° C. for 30 minutes to prepare a vulcanized rubber. The results of measuring the properties of this vulcanized rubber are also shown in Table 1. In the evaluation of vulcanized rubber properties, the viscosity specific gravity constant (VGC) is VGC=0.00743C _P +0.00925C _N +0.0110C _A ...(1) (C _P , C _N and C _A are each the paraffinic carbon percentage , naphthenic carbon percentage, and aromatic carbon percentage). JIS spring hardness and JIS rebound resilience are values measured after being left in a constant temperature room for 1 hour at each temperature. Wet skid resistance was measured by using a British portable skid tester in a tank at 25°C, and using Safety Walk (manufactured by Sumitomo 3M) to make a wet road surface with distilled water.
The measured values are expressed as an index with Comparative Example 1 set as 100, and the larger the value, the greater the skid resistance. The ice-skipped resistance was measured using a similar device in a tank at -20°C, using distilled water on a glass plate to create an icy road surface with a thickness of 2 mm, and comparing the measured value with Comparative Example 1 as 100. It is expressed as an index.

【table】

[Table] As is clear from Table 1, the vulcanization characteristics of the rubber compositions of the present invention shown in Examples 1 to 5 are such that they have the JIS rebound properties required for general road tires, as well as high wet skid resistance. This is an excellent rubber composition that improves ice skid resistance while maintaining resistance. In comparison, the rubber composition of Comparative Example 1 has a low blending ratio of styrene-butadiene copolymer rubber (SBR), and therefore has poor wet skid resistance. In addition, the rubber composition of Comparative Example 2 has a normal formulation for captreads, and white carbon is blended to improve cut resistance, but the blending ratio of styrene-butadiene copolymer rubber (SBR) is low; Moreover, since it does not contain polybutadiene rubber (BR), the balance between wet skid resistance and ice skid resistance is very poor. Furthermore, by using an extender oil with a viscosity specific gravity constant (VGC) of 0.80 to 0.93 specified in the present invention, even though a larger amount of extender oil is used than in Comparative Examples 1 and 2, which used conventional extender oils. First, it has a very low embrittlement temperature, has excellent low-temperature properties, and can suppress changes in hardness between (-20°C) and (50°C). From the test results of Examples 1 to 5 and Comparative Examples 1 to 2, it was found that in rubber compositions in which the VGC value of the total extender oil is 0.80 to 0.93, the properties after vulcanization are (1) JIS at -20℃ Spring hardness: less than 70 (2) Change in JIS spring hardness from -20℃ to 50℃: within 10 points (3) JIS rebound at 80℃: 65% or less (4) JIS rebound at 0℃ : 35% or more and 40% or less (5) Brittleness temperature: -65°C or lower, preferably -70°C or lower The rubber composition balances the driving performance on both snow/ice roads and general roads such as wet roads. We have obtained the knowledge that it is necessary to achieve good satisfaction. Example 6 and Comparative Examples 3 to 4 Pneumatic tires (tire size 1000-24 14PR) were prepared in which each of the rubber compositions of Example 1, Comparative Example 1, and Comparative Example 2 were arranged on the tread, and an actual vehicle test was conducted. The results are shown in Table 2 as an index with Comparative Example 4 as 100.

【table】

[Table] Braking test on snow and ice was -10 outside of Sapporo City.
Evaluated by the braking distance when driving at 60km/HR on a flat, compacted snow road at ℃, and the time required to climb a slope with an average slope of 7° for 200m at an initial speed of 20km/HR. It was evaluated by In addition, the wet road braking test was conducted on a water-sprinkled test road at 60km/hr.
The vehicle was evaluated based on the braking distance when the vehicle was driven and the brakes were applied. Wear life was evaluated by the distance traveled per 1 mm of tire wear thickness when driving on a dump truck with a rough road surface of 50% or more, and cut and chipping resistance was evaluated by the number of cuts and chips in the tread portion. As is clear from Table 2, when adding ice skid properties by disposing the rubber composition of Comparative Example 1 on the tread of a tire for snow and ice, not only does the wet skid property deteriorate, but the wear resistance also decreases. and the chipping resistance is significantly reduced (Comparative Example 3). On the contrary, the tire (Example 6) in which the rubber composition of the present invention obtained in Example 1 was disposed in the tread had excellent ice skid properties even though it was a general road tire. In addition, it has been found to be particularly effective as a tire for relatively large vehicles such as trucks and buses that travel on rough roads or for long periods of time, as it has high wear resistance and other characteristics such as wet skid properties are not impaired. did. From the above results, a pneumatic tire in which the rubber composition of the present invention is disposed in the tread satisfies two performances that were conventionally thought to be contradictory: braking performance on snow and ice roads and braking performance on wet roads. By satisfying the wear resistance and chipping resistance of general road tires, it is possible to drive on any road surface with a single tire, and in addition to ensuring safety, it also reduces road damage, noise, and This also greatly contributes to reducing the cost required for attaching and detaching tires and chains.

Claims (1)

[Claims] 1 Natural rubber and/or polyisoprene rubber
30 to 60 parts by weight, 5 to 40 parts by weight of polybutadiene rubber, and 30 to 60 parts by weight of styrene-butadiene copolymer rubber.
5 parts by weight of an extender oil having a viscosity specific gravity constant (VGC) of 0.80 to 0.93 to 100 parts by weight of rubber.
A tread rubber composition for heavy-duty vehicle tires, characterized in that it contains ~20 parts by weight and 45 to 60 parts by weight of carbon black.