JPH032185B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a rubber composition for tire treads, and in particular provides the rubber composition with a micro-composite structure in which a specific carbon black is unevenly distributed in a specific diene rubber, thereby improving the wet resistance of the tire tread. The present invention relates to a method for producing a rubber composition for tire tread, which has improved abrasion resistance and heat resistance in a balanced manner without reducing any of these three properties. When developing formulations for tire treads, it has recently become desirable to balance and improve both safety, such as heat resistance and wet resistance, and economic efficiency, such as abrasion resistance and rolling resistance. Summer. However, with conventional methods, improving abrasion resistance and heat resistance reduces wet resistance, and improving wet resistance and abrasion resistance reduces heat resistance. It has not been possible to improve the balance between gender and economy. In order to achieve a balanced improvement in these properties, the abrasion resistance and wet resistance are improved by using treaded rubber. Although new attempts have been made to address this issue, new problems arise such as disrupting other balances and complicating the manufacturing process, so this is not completely satisfactory. Another method described in JP-A-54-50545 is to blend polymers with different glass transition temperatures, but in this case, a polymer with a glass transition temperature of 50 to 70°C is used, resulting in a decrease in heat resistance. Application to large tires is difficult. Furthermore, according to the invention described in JP-A No. 56-32527, halogenated butyl is used as a tread rubber to improve rolling resistance, and the purpose of this is to improve the dispersion of carbon to counteract the resulting decrease in wear resistance. There is also a two-stage kneading method in which carbon black is added and kneaded in two batches, but tests conducted by the inventors have shown that this method cannot compensate for the decrease in wear resistance of large tires. It is an object of the present invention to be applicable to all tires, from small tires for motorcycles to large tires for construction vehicles, and to provide a tire that can be applied to all types of tires, from small tires such as motorcycles to large tires for construction vehicles, without reducing any of their abrasion resistance, wet resistance, and heat resistance. An object of the present invention is to provide a method for producing a rubber composition for tire tread, which can balance and significantly improve the properties of the tire. Although the object of the present invention has not yet been achieved by conventional methods as described above, the inventors have repeatedly researched the mixing of rubber and the mixing of this with carbon black. Going beyond the conventional concept of rubber composition manufacturing methods of uniformly dispersing carbon black, we have developed a rubber composition for toreading that has a micro-composite structure that maintains the reinforcing relationship between a specific rubber and a specific carbon black as much as possible even after kneading. We arrived at the idea that we should explore new possibilities for improving the performance of rubber by adding Therefore, the present invention was arrived at as a result of various studies on a method of realizing such a special micro-composite structure and how to link this to the achievement of the above-mentioned object of the present invention. This invention consists of at least two diene rubbers with glass transition temperatures different by 10°C or more and an average particle size of 5 mμ.
In the production of a vulcanizable tire tread rubber composition containing at least two different types of carbon blacks, (a) a diene rubber with a lower glass transition temperature and a carbon black with a larger average particle size are selected, and (b) selecting a diene rubber with a higher glass transition temperature and a carbon black with a smaller average particle diameter; and at least one of the following: using at least 10% by weight of the total amount of carbon black contained in the rubber composition; Production of a rubber composition for tire treads, characterized in that a diene rubber is pre-kneaded at a temperature of 120°C or higher for 30 seconds or more, and then the pre-kneaded product and the remainder of the rubber composition are further kneaded. It's a method. The diene rubbers used in this invention include natural rubber (hereinafter referred to as NR, the same hereinafter), polyisoprene rubber, cis-1,4-polybutadiene rubber (BR),
It is a homopolymer or copolymer of conjugated diene monomers such as butadiene and isoprene, which is used as tire tread rubber such as other polybutadiene rubbers and styrene-butadiene rubbers (SBR). The glass transition temperature of this rubber is measured using a differential scanning calorimeter (DSC) at a heating rate of 10° C./min. For example, the glass transition temperature measured using this method is -71°C for NR and -114°C for BR. Preferred combinations of diene rubbers with glass transition temperatures different by 10°C or more include NR/BR, SBR/NR,
There are SBR/BR etc. In these combinations, the rubber shown at the position of the fractional molecule is the diene rubber with a higher glass transition temperature. The carbon black used in this invention is a normal hard furnace black, and representative carbon blacks include ISAF, HAF, and
N339 carbon black is mentioned. The average particle size of these carbon blacks is measured using an electron microscope. The average particle diameter determined by this measurement method is 23 mμ for standard ISAF and 29 mμ for standard HAF, with the former being more than 5 mμ smaller than the latter. In this invention, the pre-kneading may be carried out by selecting diene rubber with a lower glass transition temperature and carbon black with a larger average particle size,
The diene rubber having a higher glass transition temperature and the carbon black having a smaller average particle size may be selected, or both may be used. In this case, the pre-kneading temperature and kneading time are limited to 120℃ or higher as described above, but this is done using an OOC type Banbury mixer.
Kneading was carried out for 1.5 minutes at 60 rpm and a filling rate of 70%, and the cooling hot water in the Banbury mixer was mixed at 20℃, 60℃, and
The kneading temperature is changed to 120°C, and the kneading time at 120°C or higher is determined from the temperature chart in seconds. If preliminary kneading is not carried out at a temperature of 120° C. or higher for 30 seconds or more, the object of this invention cannot be achieved. Pre-kneading is carried out as described below with reference to examples. That is, a vulcanizable tire tread rubber composition containing two types of diene rubbers, such as NR and BR, having glass transition temperatures different by 10° C. or more, and two types of carbon blacks, such as ISAF and HAF, having an average particle size different by 5 mμ or more. When manufacturing, pre-mixing is performed on BR, which has a lower glass transition temperature, and HAF, which has a larger average particle size, or NR, which has a higher glass transition temperature, and HAF, which has a smaller average particle size.
Either follow ISAF or do both. The amount of diene rubber used in preliminary kneading is BR
However, even with NR, it is necessary to use 20% by weight or more of the total amount of rubber contained in the rubber composition. The amount of carbon black used in the preliminary kneading is determined based on the total amount of carbon black contained in the rubber composition, for HAF with a larger average particle size.
It is necessary to use 15% by weight or more, and for ISAF with a smaller average particle size, 10% by weight or more. A tire tread using the rubber composition for tire leads made through preliminary mixing of the present invention has better wet resistance, abrasion resistance, and heat resistance than conventional tire treads that do not undergo such preliminary mixing. can also be improved in a balanced manner, at least without deterioration. Use carbon black with a larger average particle size for the diene rubber with a higher glass transition temperature, or conversely, use carbon black with a smaller average particle size for the diene rubber with a lower glass transition temperature. When kneading, for example, use NR/
With the combination of BR, NR and HAF or BR and
When pre-mixing is performed using ISAF, even if some of the above three properties are improved, other properties are degraded and a balanced improvement cannot be expected. If the amount of diene rubber to be pre-kneaded is less than 20% by weight of the total amount of rubber contained in the rubber composition to be manufactured, the effect of pre-kneading is small;
The effect becomes sufficiently noticeable when the amount is at least 40% by weight, and is preferably at least 40% by weight. The upper limit for the amount of diene rubber used in the pre-kneading is when the entire amount of the diene rubber is used in the pre-kneading, but this varies depending on the content of the tread rubber. In many treaded rubber formulations, this upper limit is usually 70% by weight for diene rubbers with lower glass transition temperatures and 90% by weight for diene rubbers with higher glass transition temperatures, based on the total amount of rubber in the rubber composition. It is often %. The amount of carbon black used in the preliminary kneading is 15% by weight of carbon black with a larger average particle size and 10% by weight of carbon black with a smaller average particle size, based on the total amount of carbon black contained in the rubber composition. It is necessary to use more than 15% by weight and 10% by weight, respectively, since the purpose of this invention cannot be achieved if the amount is less. Regarding the upper limit of the amount of carbon used in this preliminary kneading, as in the case of the diene rubber, up to 100% of the planned amount of carbon black can be used. After the pre-kneaded material obtained by the pre-kneading process of this invention is usually left to cool down to 30°C or below,
The missing diene rubber and carbon black are supplemented, necessary softeners, anti-aging agents, zinc white, vulcanization accelerators, etc. are added, and kneading, ie, main kneading, is performed. The thus obtained vulcanizable rubber composition for tire tread can balance and significantly improve the above-mentioned properties. Next, the present invention will be explained in more detail with reference to Examples. The test method here was as follows. In other words, the abrasion resistance tests shown in Tables 1 to 4 were conducted using a Dunlot Planbone tester according to British Standard 903.
Conducted in accordance with Part 24 Section 24.4. Tables 1-4
Heat resistance was determined using a Dunlop tripsomer tester at room temperature according to British Standard 903 Part 22.
Performed in accordance with Section 22.3. The wet resistance in Tables 1 to 4 was determined by preparing a vulcanized rubber sheet with a thickness of 6.0 mm.
This was measured at room temperature using a portable skid resistance tester manufactured by Stanley. Asphalt surface sprayed with 20°C water was selected as the contact road surface. The test results in Table 5 are the results of tests using tires, and tires were made and tested as follows for each of the rubber compositions of Comparative Example 1, Example 1, Example 4, and Reference Example 5 in Table 1. Approximately 50 kg of each of the above tire tread rubber compositions was kneaded and rolled up using a 20-inch roll, and then applied to the tread rubber of a 1000R20 14P all-steel radial tire. Wear resistance test: In this test, the four types of tire tread rubber compositions of Comparative Example 1, Example 1, Reference Example 5, and Example 4 were applied as tread rubber to the above-mentioned tire before vulcanization. Tires were used that were laminated and vulcanized on a tread for 1/4 turn in the circumferential direction of the tire. After driving the above vulcanized tires on the left and right outer sides of the drive shaft of a flat body vehicle and driving 20 laps at an average speed of 60 km on a test course of 4 km per lap, 1/4 point (point at a distance of 1/4 of the total width of the tread from the shoulder to the center of the tread)
(n= for each rubber composition)
4) After averaging the left and right sides of the shaft, the wear resistance index compared to Comparative Example 1 was calculated. Wet resistance test: The test tires were the same as the wear resistance test tires described above, except that one of the four tire tread rubber compositions was applied over the entire circumferential direction of each tire before vulcanization. Prepare in the same manner. The test is conducted by measuring the braking friction coefficient on an asphalt road surface using a trailer method. The average value of the values measured three times at a speed of 60 km/h is expressed as an index and the tire whose tread is the rubber composition of Comparative Example 1 is set as 100. Heat resistance test: The test tires are the same as in the wet resistance test. The test was conducted using a drum diameter of 1.7m.
Tire internal pressure 7.25Kg/ ^cm2 , load 2425Kg, speed 60Km/
It is shown as the internal temperature of the tread rubber at the 1/4 point after running for 1 hour at H. To measure the internal temperature, a hole with a diameter of 2 mm is drilled in advance to a depth of 10 mm from the surface at the measuring point, and the temperature is measured with a thermocouple immediately after the vehicle has finished running. Rolling resistance test: The test tires are the same as in the wet resistance test. Tested on drum diameter 1.7
After preliminary running at 100 km/h for 30 minutes with a tire internal pressure of 7.25 Kg/cm ² and a load of 2425 kg, measurements were taken at 50 km/h and 100 km/h. It is expressed as an index. Examples 1 to 4 , Comparative Example 1 , Reference Examples 1 to 5 The effect of pre-kneading in the production of rubber compositions for tire treads was evaluated using a compounding ratio of NR/BR=50/50,
The case of ISAF/HAF=25/25 was considered. Preliminary kneading was carried out using an OOC type Banbury mixer at 60 rpm and a filling rate of 70% for 1.5 minutes.
At this time, add 20% of the cooled hot water in the Banbury mixer.
℃, 60℃, and 90℃, and from the temperature chart, the kneading time at 120℃ or higher was read in seconds, and the kneading time at 120℃ or higher was determined. Next, leave the pre-kneaded rubber for about 3 hours,
℃ or less, supplement the missing diene rubber and carbon black and add aromatic oil 6.0 (all parts by weight below) and stearin so that the final composition is the same as the desired rubber composition. Acid 3.0, anti-aging agent (manufactured by Ouchi Shinko Chemical Co., Ltd., product name 810NA) 1.0, zinc white 3.0, sulfur
1.5, vulcanization accelerator (manufactured by Ouchi Shinko Chemical Co., Ltd.,
Product name MSA) 1.0 was added, and the main kneading was carried out with warm water at 50°C, filling rate 80%, and 60 rpm for 3 minutes.
After press vulcanization at 150°C for 40 minutes, an indoor test was conducted. The results are shown in Table 1.

【table】

[Table] Comparing Examples 1 to 4 of this invention and Comparative Example 1 showing the conventional manufacturing method, it is found that NR has a glass transition temperature 43°C higher than BR, but the average particle size is higher than that of HAF. It can be seen that abrasion resistance, heat resistance, and wet resistance are all improved by pre-mixing using ISAF that is 6 mμ smaller. In Example 1, BR, which has a lower glass transition temperature, is premixed with HAF, which has a larger average particle size, and the two premixes are combined, and the improvement effect is particularly remarkable. ISAF remains the same as in Reference Example 1 even after preliminary training.
When the amount of carbon black used is less than 10% by weight of the total amount of carbon black, the wet resistance decreases even if the wear resistance and heat resistance are improved. Also, in the case of preliminary training,
As in Reference Examples 2 and 3, the kneading time at 120℃ or higher is 30
If the time is less than 1 second, one of the three properties tested
2 to 2 on the contrary decreases. Also, pre-kneading was carried out as in Reference Example 4, and NR and HAF were mixed in the exact opposite way to Example 1.
Even if BR and ISAF are used in combination, there is no effect. Also, as in Reference Example 5, NR, BR,
Drilling ISAF and HAF indiscriminately all at once is ineffective. Examples 5 and 6 , Comparative Example 2 , Reference Example 6 The effect of pre-kneading was determined by mixing ratio NR/BR=90/10,
The case of ISAF/HAF=40/10 was considered.
Pre-kneading, addition of deficiencies to the final composition,
Main kneading, molding, vulcanization and testing were carried out in Examples 1 to 3.
Same as 4th prize. The results are shown in Table 2.

【table】

[Table] Example 5 has a glass transition temperature of 10°C compared to BR.
For higher NR, the average particle size is smaller than HAF.
It is a pre-kneaded ISAF smaller than 5mμ,
Example 6 is a BR with a lower glass transition temperature.
This is also pre-mixed with HAF, which has a slightly smaller amount of carbon but a larger average particle size.
Comparing these with Comparative Example 2 showing a conventional manufacturing method, it can be seen that the abrasion resistance and heat resistance are improved, and the wet resistance is also slightly improved or at least maintained at the same level. Even if pre-kneading is performed using HAF with a larger average particle size than BR with a lower glass transition temperature, as in Reference Example 6, 15% of the total amount of carbon black contained in the final compounding composition of the rubber composition is % (10% by weight in Reference Example 6) is considered to be a balanced improvement in the above properties)
The effect of this invention is not recognized. Examples 7 to 9 , Comparative Example 3 , Reference Example 7 The effect of pre-kneading was determined by mixing ratio NR/SBR=70/30,
The case of ISAF/HAF=30/20 was considered.
The operations from preliminary kneading to main kneading and vulcanization to testing were the same as in Examples 1 to 4. The results are shown in Table 3.

【table】

[Table] The glass transition temperature of SBR is 14°C higher than that of NR. Comparing Examples 7 to 9 and Comparative Example 3, which is a conventional method, there is a difference between SBR and ISAF or NR.
By pre-mixing in combination with HAF or by combining both pre-mixes, wear resistance,
It can be seen that the three properties of heat resistance and wet resistance can be improved in a balanced manner without sacrificing any deterioration of either property. Reference example 7 is SBR and
The combination of NR and carbon black is completely opposite to that of Example 9, and the wet resistance is significantly reduced. Examples 10 and 11 , Comparative Example 4 The effect of pre-kneading was determined by mixing ratio SBR/BR=80/20,
The case of ISAF/HAF=25/25 was considered.
The operations from preliminary kneading to main kneading, vulcanization, and testing were the same as in Examples 1 to 4. In this case, the glass transition temperature of SBR is 57°C higher than that of BR. The results are shown in Table 4.

【table】

[Table] Comparing Examples 10 and 11 with Comparative Example 4, which is a conventional method, it was found that the wear resistance and resistance were improved by pre-mixing SBR with ISAF, or by combining this with pre-mixing with BR and HAF. It can be seen that heat generation properties and wet resistance are balanced and significantly improved. Next, Example 1, Example 4, Comparative Example 1, Reference Example 5
Table 5 shows the results of a wear resistance test, a wet resistance test, a heat resistance test, and a rolling resistance test using the above-mentioned 1000R20 14P all-steel radial tire manufactured using a tire tread rubber composition according to the above-mentioned method. .

[Table] As shown in Examples 1 and 4, the preliminary kneading of the present invention provides a significant improvement in balance in the four properties as compared to the conventional method (Comparative Example 1). NR, BR, ISAF, HAF as in Reference Example 5
Such a balanced improvement effect would not be observed if all were pre-mixed indiscriminately. Tires made from the tire tread rubber composition produced by the pre-kneading process of this invention have excellent wet resistance and properties that could not be obtained by conventional methods.
A balanced improvement in wear resistance and heat generation resistance, that is, an improvement that does not have the disadvantage of reducing at least any of the above three properties,
This was achieved for the first time using a method that is extremely easy to implement in terms of rubber processing technology, and it is possible to improve these three properties by selecting the type and amount of diene rubber used in the preliminary mixing, the type and amount of carbon black, etc. It is possible to control the degree to some extent, and furthermore, it is possible to improve rolling resistance at the same time through appropriate selection, which is of great industrial significance.

Claims (1)

[Scope of Claims] 1. In the production of a vulcanizable tire tread rubber composition comprising at least two types of diene rubbers having glass transition temperatures different by 10°C or more and at least two types of carbon blacks having average particle diameters different by 5 mμ or more. (a) Select a diene rubber with a lower glass transition temperature and a carbon black with a larger average particle size, and set the amount of this carbon black to 15% by weight or more of the total amount of carbon black contained in the rubber composition. (b) Select a diene rubber with a higher glass transition temperature and a carbon black with a smaller average particle size, and adjust the amount of this carbon black to 10% by weight of the total amount of carbon black contained in the rubber composition. By at least one of the above methods, the diene rubber of 20% by weight or more of the total rubber contained in the rubber composition is pre-kneaded at a temperature of 120°C or more for 30 seconds or more, and then this preliminary kneading is performed. A method for producing a rubber composition for tire treads, which comprises further kneading the kneaded material and the remainder of the rubber composition.