JPS6219781B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a rubber composition for tire treads, and more specifically to a rubber compound containing a chlorine- or bromine-containing isobutylene-isoprene copolymer rubber (hereinafter referred to as halogenated butyl rubber) and a diene-based synthetic rubber and/or natural rubber. By heat-treating the composition in a high-temperature atmosphere before vulcanization, rolling resistance and heat generation are reduced without impairing the wear resistance, wet braking performance, tensile strength, and processability of unvulcanized products. The present invention relates to a method for producing a rubber composition for tire tread. Recently, there has been a strong desire for low fuel consumption in automobiles, and in particular for reduction in rolling resistance of automobile tires. However, it is said that an attempt to reduce the rolling resistance of this tire will result in a decrease in wet braking performance, and an attempt to improve the wet braking performance will result in an increase in rolling resistance and a decrease in wear resistance. In general, the performance of these tires is considered to be largely dependent on the energy loss characteristics of the tire tread rubber material, so it has been empirically shown that reducing rolling resistance, improving wet braking performance, and improving wear resistance are contradictory to each other. It is considered a material property. In order to reduce the rolling resistance of tires, tire tread rubber materials are used to reduce the energy loss caused by the load that the tire receives at the contact point with the road surface when the car is running and the repeated deformation that occurs as the tire rotates. Generally speaking, when testing rubber materials, dynamic loss characteristics such as impact resilience can be used as a guideline for rolling resistance. Furthermore, this rebound resilience also needs to be evaluated at a temperature around 70°C, taking into account the driving conditions of the car, and the higher the rebound resilience at this temperature, the lower the rolling resistance. On the other hand, in order to improve the wet braking performance of tread rubber materials, which is an important performance in terms of car safety, when a tire is braked and the road surface slides, tread rubber material can be used as a rubber material to follow the unevenness of the road surface. It is necessary that energy loss as frictional resistance caused by material deformation be large. This rubber material test for wet braking performance is carried out using the British Portable Skid Tester's wet skid resistance value. Furthermore, in addition to the above two characteristics, wear resistance is also an important characteristic from the perspective of tire economics, and while maintaining a high level of balance between rolling resistance reduction and wet braking performance, wear resistance is not significantly impaired. The development of non-treaded materials and manufacturing methods is a major issue in order to achieve energy and resource conservation. The object of the present invention is to meet such demands by reducing energy loss due to dynamic deformation of vulcanized products without impairing their wet braking performance, abrasion resistance, tensile strength, or processability when uncured. It is an object of the present invention to provide a method for producing a rubber composition for tire tread that reduces dynamic resistance and heat generation. The present inventors have conducted various studies with the aim of obtaining a rubber composition for tire treads that satisfies this demand. Among them, R.C. Keller (R.
C. Keller) [Improvement of
Improvement of Tire Traction wich
Tire Science and Technology
Technology) 1 (2) May (1973) pages 190-201] and JP-A-55-135148, which was previously invented by some of the present inventors, halogenated butyl rubber is used as a raw material rubber. A rubber composition made by blending natural rubber or polyisoprene rubber and polybutadiene rubber in a certain ratio provides a good balance between the two properties (rolling resistance and wet braking performance) and abrasion resistance of the vulcanized product. be. As a result of a more detailed study of the mixing blend system of the rubber composition, the present inventors found that the maximum temperature of the rubber composition during mixing or the temperature at the time of release was 180 to 220.
It has been found that the impact resilience is significantly improved by raising the temperature to a high temperature of °C. In the process of kneading rubber compositions, the mixing temperature is
It is one of the important factors affecting the working efficiency and physical properties of the mixture. Generally, the higher the temperature,
The viscosity of the rubber mixture is reduced, and less mechanical energy is required for mixing, but the shearing force acting on the raw rubber is also reduced, making it less efficient to disperse carbon black and other compounding agents into the raw rubber. Become. Furthermore, if the temperature during mixing is high, the decomposition of the raw rubber molecular chains increases and the molecular weight decreases, resulting in a decrease in the strength and physical properties of the vulcanizate. Therefore, when mixing in a normal internal mixer, careful attention must be paid to the filling rate, mixing order, cooling of the rotor, casing, etc. so that the mixing temperature does not become too high. In the manufacturing method of the present invention, even if the mixing temperature during kneading is 180°C or higher, the impact resilience of the vulcanizate can be improved without impairing the vulcanization properties such as tensile strength and wet skid resistance, and the processability can be improved. Nor. However, if the mixing temperature exceeds 220°C, thermal deterioration of the rubber will occur and the physical properties of the rubber will deteriorate, which is not preferable. The present invention provides chlorine- or bromine-containing isobutylene.
A rubber mixture consisting of a raw material rubber containing at least 5 to 30% by weight of isoprene copolymer rubber (halogenated butyl rubber) and other compounding ingredients excluding the vulcanization accelerator and sulfur (before blending the vulcanization accelerator and sulfur). This is a method for producing a rubber composition for tire treads, which comprises heat-treating a rubber composition (a rubber composition) at a temperature of 180 to 220°C, and then blending a vulcanization accelerator and sulfur. The raw material rubber used in the present invention needs to contain 5 to 30% by weight of halogenated butyl rubber, and if the content of halogenated butyl rubber in the raw material rubber is less than 5% by weight, impact resilience can be improved by heat treatment at 180°C or higher. effect cannot be achieved. Also 30% by weight
Exceeding this is not preferable because the heat generation property of the rubber increases and the abrasion resistance decreases. Raw material rubbers other than halogenated butyl rubber include diene synthetic rubber and/or
Or natural rubber is used. The preferred blending ratio of the raw material rubber is as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 135148/1986, 5 to 30% by weight of halogenated butyl rubber, 40 to 95% by weight of natural rubber and/or polyisoprene rubber, and polybutadiene rubber. If a rubber composition containing raw material rubber in such a range is used in the present invention, the impact resilience of the vulcanizate will further increase, so the rolling resistance will be improved. can be further reduced without impairing other properties. The heat treatment at a temperature of 180 to 220°C in the present invention is achieved by the following method. (1) By extending the mixing time or increasing the side wall chamber temperature in the mixing stage (first stage mixing) before mixing the vulcanization accelerator and sulfur, the maximum temperature of the rubber mixture or at the time of release can be increased. temperature of 180
(2) The first stage is mixed in the conventional manner, and then the rubber mixture is kneaded to a temperature of 180°C.
(3) After mixing the rubber mixture using the conventional mixing method, place it in an atmosphere with a temperature of 180 to 220℃ without kneading, and bring the temperature of the entire rubber mixture to 180℃.
-220°C, etc., and in both cases, the temperature is 180-220°C without containing a vulcanization accelerator and sulfur. The above-mentioned Japanese Patent Application Laid-Open No. 55-1997-1 contains halogenated butyl rubber, natural rubber and/or polyisoprene rubber, and polybutadiene rubber in specific proportions, respectively.
Rubber compositions such as those disclosed in No. 135148 generally tend to stick to metal rolls and the like, and in particular, when heat treated as in the present invention, the stickiness increases further and roll kneading operations may become difficult. This processing problem is solved by adding to the rubber composition a process oil containing more than 40% by weight of paraffin components. In other words, adding a process oil with a paraffin content of 40% by weight or more not only reduces adhesion to metals and makes processing easier, but also improves rebound resilience without impairing vulcanizate properties, abrasion resistance, etc. It is preferably used in the present invention because it can increase the temperature and suppress heat generation.
This process oil may have a paraffin component of 40% by weight or more and may be used alone, or it may be blended with one with a high paraffin component and one with a low paraffin component so that the total paraffin component is 40% by weight or more. Good too. Further, the addition of such process oil becomes significant when 5 parts by weight or more is used per 100 parts by weight of the total amount of raw rubber. In addition to the process oil described above, compounding agents commonly used in the rubber industry, such as sulfur, vulcanization accelerators, zinc oxide, vulcanization aids, anti-aging agents, etc., may be appropriately added to the rubber composition of the present invention. I can do it. Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples. All formulations in the table are parts by weight. Examples 1 to 3 and Comparative Examples 1 to 9 Rubber compositions having the formulations shown in Table 1 were mixed in the following manner. Small internal mixer (volume 1.7
), the initial side wall temperature was set at 50 to 60° C., the rotor rotation speed was set at 40 rpm, the raw rubber components were first introduced, and after mixing for 30 seconds, the vulcanization accelerator and the compounding agents excluding sulfur were added. The mixing time was 4 minutes and 30 seconds, and during this time the cooling water or heating steam was controlled so that the temperature reached the predetermined temperature listed in Table 1. A vulcanization accelerator and sulfur were blended into a rubber mixture consisting of this raw rubber and compounding agents, and the mixture was kneaded for 4 minutes using 8-inch rolls adjusted to 60°C. This rubber composition was heated to 160°C.
The properties of the vulcanizate were evaluated. The results are shown in Table 1. Note that the characteristics of the vulcanizate were evaluated by the following method. Tensile strength, elongation, 300% tensile stress, and impact resilience were measured in accordance with JIS K6301, and Liupke impact resilience was used for impact resilience. Note that the larger the impact resilience value, the lower the rolling resistance of the vulcanized product. In addition, the heat generation test was evaluated by temperature rise using a Gutsudoritsu flexometer test. Abrasion resistance was measured using a Gutdritsu Pico abrasion tester, and wet skid resistance was measured using a British Portable Skid Tester (manufactured by Stanley, used on 3M road surface).
Outdoor Type B Safety Walk, Temperature 25
℃, ASTM E303-74) are shown as indexes for each group, that is, Group is Comparative Example 1, Group is Comparative Example 4, Group is Comparative Example 6, and Group is Comparative Example 9, each with 100. It was evaluated using the index. The abrasion resistance determined by the Pico abrasion test is an indicator of the abrasion resistance of vulcanized products, especially tires, and the higher the abrasion resistance index, the better the abrasion resistance. Wet skid resistance is an index of the wet braking performance of a vulcanized product, and the higher the index of wet skid resistance, the better the wet braking performance.

[Table] The first group (Comparative Examples 1 to 3) uses only styrene-butadiene copolymer rubber (SBR) as the raw material rubber, and only changes the rubber temperature immediately after mixing and releasing (hereinafter referred to as mixing and releasing rubber temperature). However, as the temperature increases, the impact resilience does not increase, and the tensile strength and elongation decrease. The third group (Comparative Examples 4 to 5) uses only natural rubber (NR) as the raw material rubber and only changes the temperature of the mixed release rubber.As the temperature increases, the impact resilience improves and heat generation decreases. , tensile strength, elongation and abrasion resistance are significantly reduced. Group (Comparative Examples 6-8 and Examples 1-
2) uses chlorinated butyl rubber (Cl-IIR), natural rubber, and polybutadiene rubber (BR) as raw rubbers, and the higher the mixed release rubber temperature, the higher the rebound resilience and the lower the heat generation. In particular, this tendency was observed in Example 1 and Example 1 where the temperature of the released rubber was 180℃.
This is remarkable in Example 2 where the temperature was 200°C. In addition, in this case, the tensile strength and abrasion resistance hardly decrease. The third group (Comparative Example 9, Example 3) uses styrene-butadiene copolymer rubber, polybutadiene rubber, and chlorinated butyl rubber as raw materials and changes the mixing and releasing temperature. In Example 3, as compared to Comparative Example 9 (mixing release temperature 140° C.), impact resilience and heat generation properties were improved without impairing tensile strength and abrasion resistance. This shows that in a rubber composition containing halogenated butyl rubber as a raw material rubber, when the mixing and release temperature is increased, the impact resilience and heat generation property are improved, and other properties are not impaired. Examples 4 to 7 and Comparative Examples 10 to 11 The rubber compositions having the formulations shown in Table 2 were heat treated in the following manner. In Example 4, the first stage was mixed in the conventional manner (mixing temperature 140°C), and then the rubber temperature was brought to 180°C by kneading operation.
The first stage is mixed as usual (mixing temperature
160°C) and then placed in an oven at 180°C for 30 minutes. Further, Examples 6 to 7 and Comparative Examples 10 to 11 were heat-treated to a predetermined temperature in the same manner as in Example 1. A vulcanization accelerator and sulfur were added to a rubber mixture excluding these vulcanization accelerators and sulfur and kneaded to obtain a rubber composition. This rubber composition was press vulcanized and the properties of the vulcanized product were evaluated. The results are shown in Table 2. The kneading conditions, vulcanization conditions, and property evaluation method were the same as in Comparative Example 1. Furthermore, the abrasion resistance and wet skid resistance were expressed as an index with Comparative Example 6 set as 100.

【table】

[Table] Examples 4 and 5 have the same formulation as Example 1, but differ from Example 1 in that the rubber mixture was heat-treated at 180° C. before adding the vulcanization accelerator and sulfur. Examples 4 and 5 exhibit the same vulcanization characteristics as Example 1, and have improved impact resilience and reduced heat generation compared to Comparative Examples 6 and 7. Comparative Example 10 and Example 6 are groups, i.e., NR/BR/Cl-IIR rubber compositions, with different mixing ratios of raw rubber, but Example 6, which was heat-treated at 180°C, was heat-treated at 140°C. Compared to Comparative Example 10, it has higher impact resilience and lower heat generation. This was similarly proven in Comparative Example 11 and Example 7 in which the blending ratio of NR/BR/Cl-IIR was 40/35/25. From the above, NR/BR/Cl-IIR rubber compositions are heated to 180°C before adding the vulcanization accelerator and sulfur.
It has been found that when heat-treated as described above, the impact resilience and exothermic properties of the vulcanizate are significantly improved, and other vulcanization properties are not impaired, regardless of the heat treatment method. Examples 1, 8 to 9 The compounding ingredients shown in Table 1 excluding the vulcanization accelerator and sulfur were mixed with the raw rubber and heat treated at 180°C, then the vulcanization accelerator and sulfur were mixed and kneaded to obtain a rubber composition. I got something. This rubber composition was press-vulcanized and the properties of the vulcanized product were evaluated. The results are shown in Table 3. The kneading conditions, vulcanization conditions, and vulcanization characteristics evaluation method were the same as in Comparative Example 1. For unvulcanized processability, rubber is wrapped around an 8-inch roll adjusted to 60°C, and the degree of adhesion to the roll surface is evaluated on a five-point scale. The lower the number, the stronger the adhesion and the worse the workability. The weight percentage of the paraffin component in the process oil was determined by determining the viscosity specific gravity constant (VGC) and the refraction intercept, and applying it to the triangular diagram of ATSM D 2140. Furthermore, the abrasion resistance and wet skid resistance are expressed as an index with Comparative Example 6 set as 100.

【table】

[Table] %, manufactured by Showa Sekiyu Co., Ltd.)
In Example 1, the mixed release rubber temperature was adjusted as described above.
Setting the temperature to 180°C improves rebound resilience and reduces heat generation without impairing other vulcanization properties, but there are some difficulties in processability when unvulcanized. In Example 8, the paraffin component in the process oil was 38% by weight, but the processability when unvulcanized was somewhat improved. Further, in Example 9, in which the paraffin component was 48% by weight, not only the workability when unvulcanized was greatly improved compared to Example 1, but also the impact resilience was further improved and heat generation was further suppressed. Also, other vulcanization properties are not impaired. Therefore, in rubber compositions using NR/BR/Cl-IIR as raw material rubber, if a process oil containing a large amount of paraffin component, especially 40% by weight or more, is added, the processability when unvulcanized is improved. It can be seen that it not only improves vulcanization, but also improves rebound resilience and suppresses heat generation without impairing other vulcanization properties. As explained above, in a rubber composition using diene-based synthetic rubber containing halogenated butyl rubber and/or natural rubber as a raw material rubber, 180%
The vulcanizate produced by the production method of the present invention, which is heat-treated at a high temperature of ~220°C, has improved rebound resilience and can suppress heat generation without impairing properties such as tensile strength or abrasion resistance. Especially NR/BR/Hal-IIR
By adding process oil containing a large amount of paraffin components,
The above-mentioned effect becomes even more remarkable, and the processability when unvulcanized is also greatly improved. When the vulcanizate obtained by the method of the present invention, which has such effects, is used in the tread part of a tire, it reduces rolling resistance compared to conventional tires, and has excellent wear resistance and braking on wet roads. It is preferably used because it does not impair performance.

Claims (1)

[Scope of Claims] 1. A rubber mixture consisting of a raw material rubber containing 5 to 30% by weight of isobutylene/isoprene copolymer rubber containing chlorine or bromine, and a vulcanization accelerator and other compounding ingredients excluding sulfur. 1. A method for producing a rubber composition for tire treads, which comprises adding a vulcanization accelerator and sulfur after heat treatment at a temperature of 220°C. 2. The raw material rubber is 5 to 30% by weight of isobutylene/isoprene copolymer rubber containing chlorine or bromine, 40 to 95% by weight of natural rubber or polyisoprene rubber, and 50% by weight or less of polybutadiene rubber. A method for producing the rubber composition for tire treads as described above. 3 Among the other compounding ingredients, process oil is the raw material rubber.
The method for producing a rubber composition for tire tread according to claim 1 or 2, wherein 5 parts by weight or more is blended with respect to 100 parts by weight, and the paraffin component in the process oil is 40% by weight or more. .